as defined in section 3.2. Resources may be available in multiple representations (e.g. multiple languages, data formats, size, and resolutions) or vary in other ways.
entity The information transferred as the payload of a request or response. An entity consists of metainformation in the form of entity-header fields and content in the form of an entity-body, as described in section 7.
representation An entity included with a response that is subject to content negotiation, as described in section 12. There may exist multiple representations associated with a particular response status.
content negotiation The mechanism for selecting the appropriate representation when servicing a request, as described in section 12. The representation of entities in any response can be negotiated (including error responses).
variant A resource may have one, or more than one, representation(s) associated with it at any given instant. Each of these representations is termed a `varriant'. Use of the term `variant' does not necessarily imply that the resource is subject to content negotiation.
client A program that establishes connections for the purpose of sending requests.
user agent The client which initiates a request. These are often browsers, editors, spiders (web-traversing robots), or other end user tools.
server An application program that accepts connections in order to service requests by sending back responses. Any given program may be capable of being both a client and a server; our use of these terms refers only to the role being performed by the program for a particular connection, rather than to the program's capabilities in general. Likewise, any server may act as an origin server, proxy, gateway, or tunnel, switching behavior based on the nature of each request.
origin server The server on which a given resource resides or is to be created.
proxy An intermediary program which acts as both a server and a client for the purpose of making requests on behalf of other clients. Requests are serviced internally or by passing them on, with possible translation, to other servers. A proxy MUST implement both the client and server requirements of this specification. A "transparent proxy" is a proxy that does not modify the request or response beyond what is required for proxy authentication and identification. A "non-transparent proxy" is a proxy that modifies the request or response in order to provide some added service to the user agent, such as group annotation services, media type transformation, protocol reduction, or anonymity filtering. Except where either transparent or non-transparent behavior is explicitly stated, the HTTP proxy requirements apply to both types of proxies.
gateway A server which acts as an intermediary for some other server.
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