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<title>Glossary - Apache HTTP Server Version 2.5</title>
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<p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/quickreference.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p>
<p class="apache">Apache HTTP Server Version 2.5</p>
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="./">Version 2.5</a></div><div id="page-content"><div id="preamble"><h1>Glossary</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="/de/glossary.html" hreflang="de" rel="alternate" title="Deutsch"> de </a> |
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<p>This glossary defines some of the common terminology related to Apache in
particular, and web serving in general. More information on each concept
is provided in the links.</p>
</div>
<div class="section">
<h2><a name="definitions" id="definitions">Definitions</a></h2>
<dl>
<dt><a name="accesscontrol" id="accesscontrol">Access Control</a></dt>
<dd>The restriction of access to network realms. In an Apache context
usually the restriction of access to certain <em>URLs</em>.<br /> See: <a href="howto/auth.html">Authentication, Authorization, and Access
Control</a>
</dd>
<dt><a name="algorithm" id="algorithm">Algorithm</a></dt>
<dd>An unambiguous formula or set of rules for solving a problem in a finite
number of steps. Algorithms for encryption are usually called
<dfn>Ciphers</dfn>.
</dd>
<dt><a name="apacheextensiontool" id="apacheextensiontool">APache
eXtension Tool</a> <a name="apxs" id="apxs">(apxs)</a></dt>
<dd>A perl script that aids in compiling <a class="glossarylink" href="/glossary.html#module" title="see glossary">module</a> sources into Dynamic Shared Objects
(<a class="glossarylink" href="/glossary.html#dso" title="see glossary">DSO</a>s) and helps install them in the
Apache Web server.<br />
</dd>
<dt><a name="apacheportableruntime" id="apacheportableruntime">Apache Portable Runtime</a> <a name="apr" id="apr">(APR)</a></dt>
<dd>A set of libraries providing many of the basic interfaces
between the server and the operating system. APR is developed
parallel to the Apache HTTP Server as an independent project.<br />
See: <a href="http://apr.apache.org/">Apache Portable Runtime
Project</a>
</dd>
<dt><a name="authentication" id="authentication">Authentication</a></dt>
<dd>The positive identification of a network entity such as a server, a
client, or a user.<br />
Control</a>
</dd>
<dt><a name="certificate" id="certificate">Certificate</a></dt>
<dd>A data record used for authenticating network entities such
as a server or a client. A certificate contains X.509 information pieces
about its owner (called the subject) and the signing <a class="glossarylink" href="/glossary.html#certificationauthority" title="see glossary">Certification Authority</a> (called
the issuer), plus the owner's <a class="glossarylink" href="/glossary.html#publickey" title="see glossary">public
key</a> and the
signature made by the CA. Network entities verify these signatures
using CA certificates.<br />
</dd>
<dt><a name="certificatsigningrequest" id="certificatsigningrequest">Certificate Signing Request</a>
<a name="csr" id="csr">(CSR)</a></dt>
<dd>An unsigned <a class="glossarylink" href="/glossary.html#certificate" title="see glossary">certificate</a> for
submission to a <a class="glossarylink" href="/glossary.html#certificationauthority" title="see glossary">Certification
Authority</a>, which signs it with the <a class="glossarylink" href="/glossary.html#privatekey" title="see glossary">Private Key</a> of their CA
<em>Certificate</em>. Once the CSR is signed, it becomes a real
certificate.<br />
</dd>
<dt><a name="certificationauthority" id="certificationauthority">Certification Authority</a>
<a name="ca" id="ca">(CA)</a></dt>
<dd>A trusted third party whose purpose is to sign certificates for network
entities it has authenticated using secure means. Other network entities
can check the signature to verify that a CA has authenticated the bearer
of a certificate.<br />
</dd>
<dt><a name="cipher" id="cipher">Cipher</a></dt>
<dd>An algorithm or system for data encryption. Examples are DES, IDEA, RC4,
etc.<br />
</dd>
<dt><a name="ciphertext" id="ciphertext">Ciphertext</a></dt>
<dd>The result after <a class="glossarylink" href="/glossary.html#plaintext" title="see glossary">Plaintext</a> is
passed through a <a class="glossarylink" href="/glossary.html#cipher" title="see glossary">Cipher</a>.<br /> See: <a href="ssl/">SSL/TLS Encryption</a>
</dd>
<dt><a name="commongatewayinterface" id="commongatewayinterface">Common
Gateway Interface</a> <a name="cgi" id="cgi">(CGI)</a></dt>
<dd>A standard definition for an interface between a web server and an
external program that allows the external program to service requests.
There is an <a href="http://www.ietf.org/rfc/rfc3875">Informational
RFC</a> which covers the specifics.<br />
</dd>
<dt><a name="configurationdirective" id="configurationdirective">Configuration Directive</a></dt>
<dd>See: <a class="glossarylink" href="/glossary.html#directive" title="see glossary">Directive</a></dd>
<dt><a name="configurationfile" id="configurationfile">Configuration
File</a></dt>
<dd>A text file containing <a class="glossarylink" href="/glossary.html#directive" title="see glossary">Directives</a>
that control the configuration of Apache.<br />
</dd>
<dt><a name="connect" id="connect">CONNECT</a></dt>
<dd>An HTTP <a class="glossarylink" href="/glossary.html#method" title="see glossary">method</a> for proxying raw data
channels over HTTP. It can be used to encapsulate other protocols, such as
the SSL protocol.
</dd>
<dt><a name="context" id="context">Context</a></dt>
<dd>An area in the <a class="glossarylink" href="/glossary.html#configurationfile" title="see glossary">configuration
files</a> where certain types of <a class="glossarylink" href="/glossary.html#directive" title="see glossary">directives</a> are allowed.<br />
See: <a href="mod/directive-dict.html#Context">Terms Used to Describe
Apache Directives</a>
</dd>
<dt><a name="digitalsignature" id="digitalsignature">Digital
Signature</a></dt>
<dd>An encrypted text block that validates a certificate or other file. A
<a class="glossarylink" href="/glossary.html#certificationauthority" title="see glossary">Certification Authority</a>
creates a signature by generating a hash of the <em>Public Key</em>
embedded in a <em>Certificate</em>, then encrypting the hash with its own
<em>Private Key</em>. Only the CA's public key can decrypt the signature,
verifying that the CA has authenticated the network entity that owns the
<em>Certificate</em>.<br />
</dd>
<dt><a name="directive" id="directive">Directive</a></dt>
<dd>A configuration command that controls one or more aspects of Apache's
behavior. Directives are placed in the <a class="glossarylink" href="/glossary.html#configurationfile" title="see glossary">Configuration File</a><br />
</dd>
<dt><a name="dynamicsharedobject" id="dynamicsharedobject">Dynamic
Shared Object</a> <a name="dso" id="dso">(DSO)</a></dt>
<dd><a class="glossarylink" href="/glossary.html#module" title="see glossary">Modules</a> compiled separately from the
Apache <code class="program"><a href="/programs/httpd.html">httpd</a></code> binary that can be loaded on-demand.<br />
</dd>
<dt><a name="environmentvariable" id="environmentvariable">Environment
Variable</a> <a name="env-variable" id="env-variable">(env-variable)</a></dt>
<dd>Named variables managed by the operating system shell and used to store
information and communicate between programs. Apache also contains
internal variables that are referred to as environment variables, but are
stored in internal Apache structures, rather than in the shell
environment.<br />
</dd>
<dt><a name="export-crippled" id="export-crippled">Export-Crippled</a></dt>
<dd>Diminished in cryptographic strength (and security) in order to comply
with the United States' Export Administration Regulations (EAR).
Export-crippled cryptographic software is limited to a small key size,
resulting in <em>Ciphertext</em> which usually can be decrypted by brute
force.<br />
</dd>
<dt><a name="filter" id="filter">Filter</a></dt>
<dd>A process that is applied to data that is sent or received by the
server. Input filters process data sent by the client to the server,
while output filters process documents on the server before they are sent
to the client. For example, the <code>INCLUDES</code> output filter
processes documents for <a class="glossarylink" href="/glossary.html#ssi" title="see glossary">Server Side
Includes</a>.<br />
</dd>
<dt><a name="fully-qualifieddomain-name" id="fully-qualifieddomain-name">Fully-Qualified Domain-Name</a>
<a name="fqdn" id="fqdn">(FQDN)</a></dt>
<dd>The unique name of a network entity, consisting of a hostname and a
domain name that can resolve to an IP address. For example,
</dd>
<dt><a name="handler" id="handler">Handler</a></dt>
<dd>An internal Apache representation of the action to be performed when a
file is called. Generally, files have implicit handlers, based on the file
type. Normally, all files are simply served by the server, but certain
file types are "handled" separately. For example, the
<code>cgi-script</code> handler designates files to be processed as
</dd>
<dt><a name="hash" id="hash">Hash</a></dt>
<dd>A mathematical one-way, irreversible algorithm generating a string with
fixed-length from another string of any length. Different input strings
will usually produce different hashes (depending on the hash function).
</dd>
<dt><a name="header" id="header">Header</a></dt>
<dd>The part of the <a class="glossarylink" href="/glossary.html#http" title="see glossary">HTTP</a> request and
response that is sent before the actual content, and that contains
meta-information describing the content.
</dd>
<dt><a name="htaccess" id="htaccess">.htaccess</a></dt>
<dd>A <a class="glossarylink" href="/glossary.html#configurationfile" title="see glossary">configuration file</a> that
is placed inside the web tree and applies configuration <a class="glossarylink" href="/glossary.html#directive" title="see glossary">directives</a> to the directory where it is
placed and all sub-directories. Despite its name, this file can hold
almost any type of directive, not just access-control directives.<br />
</dd>
<dd>The main Apache <a class="glossarylink" href="/glossary.html#configurationfile" title="see glossary">configuration
file</a>. The default location is
run-time or compile-time configuration.<br />
</dd>
<dt><a name="hypertexttransferprotocol" id="hypertexttransferprotocol">HyperText Transfer Protocol</a>
<a name="http" id="hhtp">(HTTP)</a></dt>
<dd>The standard transmission protocol used on the World Wide Web. Apache
</dd>
<dt><a name="https" id="https">HTTPS</a></dt>
<dd>The HyperText Transfer Protocol (Secure), the standard encrypted
communication mechanism on the World Wide Web. This is actually just HTTP
</dd>
<dt><a name="method" id="method">Method</a></dt>
<dd>In the context of <a class="glossarylink" href="/glossary.html#http" title="see glossary">HTTP</a>, an action to
perform on a resource, specified on the request line by the client. Some
of the methods available in HTTP are <code>GET</code>, <code>POST</code>,
and <code>PUT</code>.
</dd>
<dt><a name="messagedigest" id="messagedigest">Message Digest</a></dt>
<dd>A hash of a message, which can be used to verify that the contents of
the message have not been altered in transit.<br />
</dd>
<dt><a name="mime-type" id="mime-type">MIME-type</a></dt>
<dd>A way to describe the kind of document being transmitted. Its name
comes from that fact that its format is borrowed from the Multipurpose
Internet Mail Extensions. It consists of a major type and a minor type,
HTTP, the MIME-type is transmitted in the <code>Content-Type</code>
</dd>
<dt><a name="module" id="module">Module</a></dt>
<dd>An independent part of a program. Much of Apache's functionality is
contained in modules that you can choose to include or exclude. Modules
that are compiled into the Apache <code class="program"><a href="/programs/httpd.html">httpd</a></code> binary are
called <dfn>static modules</dfn>, while modules that are stored
separately and can be optionally loaded at run-time are called
<dfn>dynamic modules</dfn> or <a class="glossarylink" href="/glossary.html#dso" title="see glossary">DSOs</a>.
Modules that are included by default
are called <dfn>base modules</dfn>. Many modules are available for Apache
that are not distributed as part of the Apache HTTP Server <a class="glossarylink" href="/glossary.html#tarball" title="see glossary">tarball</a>. These are referred to as
<dfn>third-party modules</dfn>.<br />
See: <a href="mod/">Module Index</a>
</dd>
<dt><a name="modulemagicnumber" id="modulemagicnumber">Module Magic
Number</a> (<a name="mmn" id="mmn">MMN</a>)</dt>
<dd>Module Magic Number is a constant defined in the Apache source code that
is associated with binary compatibility of modules. It is changed when
internal Apache structures, function calls and other significant parts of
API change in such a way that binary compatibility cannot be guaranteed
any more. On MMN change, all third party modules have to be at least
recompiled, sometimes even slightly changed in order to work with the new
version of Apache.
</dd>
<dt><a name="openssl" id="openssl">OpenSSL</a></dt>
</dd>
<dt><a name="passphrase" id="passphrase">Pass Phrase</a></dt>
<dd>The word or phrase that protects private key files. It prevents
unauthorized users from encrypting them. Usually it's just the secret
encryption/decryption key used for <a class="glossarylink" href="/glossary.html#cipher" title="see glossary">Ciphers</a>.<br />
</dd>
<dt><a name="plaintext" id="plaintext">Plaintext</a></dt>
<dd>The unencrypted text.</dd>
<dt><a name="privatekey" id="privatekey">Private Key</a></dt>
<dd>The secret key in a <a class="glossarylink" href="/glossary.html#publickeycryptography" title="see glossary">Public Key
Cryptography</a> system, used to decrypt incoming messages and
sign outgoing ones.<br />
</dd>
<dt><a name="proxy" id="proxy">Proxy</a></dt>
<dd>An intermediate server that sits between the client and the <em>origin
server</em>. It accepts requests from clients, transmits those requests
on to the origin server, and then returns the response from the origin
server to the client. If several clients request the same content, the
proxy can deliver that content from its cache, rather than requesting it
from the origin server each time, thereby reducing response time.<br />
</dd>
<dt><a name="publickey" id="publickey">Public Key</a></dt>
<dd>The publicly available key in a <a class="glossarylink" href="/glossary.html#publickeycryptography" title="see glossary">Public Key Cryptography</a> system,
used to encrypt messages bound for its owner and to decrypt signatures
made by its owner.<br />
</dd>
<dt><a name="publickeycryptography" id="publickeycryptography">Public Key Cryptography</a></dt>
<dd>The study and application of asymmetric encryption systems, which use
one key for encryption and another for decryption. A corresponding pair of
such keys constitutes a key pair. Also called Asymmetric Cryptography.
<br />
</dd>
<dt><a name="regularexpresion" id="regularexpresion">Regular Expression</a>
<a name="regex" id="regex">(Regex)</a></dt>
<dd>A way of describing a pattern in text - for example, "all the words that
begin with the letter A" or "every 10-digit phone number" or even "Every
sentence with two commas in it, and no capital letter Q". Regular
expressions are useful in Apache because they let you apply certain
attributes against collections of files or resources in very flexible ways
- for example, all .gif and .jpg files under any "images" directory could
be written as "<code>/images/.*(jpg|gif)$</code>". In places where
regular expressions are used to replace strings, the special variables
$1 ... $9 contain backreferences to the grouped parts (in parentheses) of
the matched expression. The special variable $0 contains a backreference
to the whole matched expression. To write a literal dollar sign in a
replacement string, it can be escaped with a backslash. Historically, the
variable & could be used as alias for $0 in some places. This is no
longer possible since version 2.3.6. Apache uses Perl Compatible Regular
library. You can find more documentation about PCRE's regular expression
syntax at that site, or at
</dd>
<dt><a name="reverseproxy" id="reverseproxy">Reverse Proxy</a></dt>
<dd>A <a class="glossarylink" href="/glossary.html#proxy" title="see glossary">proxy</a> server that appears to the client
as if it is an <em>origin server</em>. This is useful to hide the real
origin server from the client for security reasons, or to load balance.
</dd>
<dt><a name="securesocketslayer" id="securesocketslayer">Secure Sockets
Layer</a> <a name="ssl" id="ssl">(SSL)</a></dt>
<dd>A protocol created by Netscape Communications Corporation for general
over SSL.<br />
</dd>
<dt><a name="servernameindication" id="servernameindication">Server Name
Indication</a> <a name="sni" id="sni">(SNI)</a></dt>
<dd>An SSL function that allows passing the desired server
hostname in the initial SSL handshake message, so that the web
server can select the correct virtual host configuration to use
in processing the SSL handshake. It was added to SSL starting
with the TLS extensions, RFC 3546. <br />
</dd>
<dt><a name="serversideincludes" id="serversideincludes">Server Side
Includes</a> <a name="ssi" id="ssi">(SSI)</a></dt>
<dd>A technique for embedding processing directives inside HTML files.<br />
</dd>
<dt><a name="session" id="session">Session</a></dt>
<dd>The context information of a communication in general.</dd>
<dt><a name="ssleay" id="ssleay">SSLeay</a></dt>
Young
</dd>
<dt><a name="subrequest" id="subrequest">Subrequest</a></dt>
<dd>Apache provides a subrequest API to modules that allows other
filesystem or URL paths to be partially or fully evaluated by
the server. Example consumers of this API are
<code class="module"><a href="/mod/mod_autoindex.html">mod_autoindex</a></code>, and <code class="module"><a href="/mod/mod_include.html">mod_include</a></code>.
</dd>
<dt><a name="symmetriccryptophraphy" id="symmetriccryptophraphy">Symmetric
Cryptography</a></dt>
<dd>The study and application of <em>Ciphers</em> that use a single secret key
for both encryption and decryption operations.<br />
</dd>
<dt><a name="tarball" id="tarball">Tarball</a></dt>
<dd>A package of files gathered together using the <code>tar</code> utility.
Apache distributions are stored in compressed tar archives or using
pkzip.
</dd>
<dt><a name="transportlayersecurity" id="transportlayersecurity">Transport
Layer Security</a> <a name="tls" id="tls">(TLS)</a></dt>
<dd>The successor protocol to SSL, created by the Internet Engineering Task
Force (IETF) for general communication authentication and encryption over
</dd>
<dt><a name="uniformresourcelocator" id="uniformresourcelocator">Uniform
Resource Locator</a> <a name="url" id="url">(URL)</a></dt>
informal term for what is formally called a <a class="glossarylink" href="/glossary.html#uniformresourceidentifier" title="see glossary">Uniform Resource Identifier</a>.
URLs are usually made up of a scheme, like <code>http</code> or
<code>https</code>, a hostname, and a path. A URL for this page might
</dd>
<dt><a name="uniformresourceidentifier" id="uniformresourceidentifier">Uniform Resource Identifier</a>
<a name="URI" id="URI">(URI)</a></dt>
<dd>A compact string of characters for identifying an abstract or physical
resource. It is formally defined by <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>. URIs used on the
world-wide web are commonly referred to as <a class="glossarylink" href="/glossary.html#url" title="see glossary">URLs</a>.
</dd>
<dt><a name="virtualhosting" id="virtualhosting">Virtual Hosting</a></dt>
<dd>Serving multiple websites using a single instance of Apache. <em>IP
virtual hosting</em> differentiates between websites based on their IP
address, while <em>name-based virtual hosting</em> uses only the name of the
host and can therefore host many sites on the same IP address.<br />
See: <a href="vhosts/">Apache Virtual Host documentation</a>
</dd>
<dt><a name="x.509" id="x.509">X.509</a></dt>
<dd>An authentication certificate scheme recommended by the International
Telecommunication Union (ITU-T) which is used for SSL/TLS authentication.<br /> See: <a href="ssl/">SSL/TLS Encryption</a>
</dd>
</dl>
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