1. Introduction

1.3 Terminology

connection

A virtual circuit established between two parties for the purpose of communication.

message

A structured sequence of octets transmitted via the connection as the basic component of communication.

request

An HTTP request message (as defined in Section 5).

response

An HTTP response message (as defined in Section 6).

resource

A network data object or service which can be identified by a URI.

entity

A particular representation or rendition of a resource that may be enclosed within a request or response message. An entity consists of metainformation (in the form of entity headers) and content (in the form of an entity body).

client

A program that establishes connections for the purpose of sending requests.

user agent

The client program which is closest to the user and which initiates requests at their behest.

server

A program that accepts connections in order to service requests by sending back responses.

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 forwarding requests. Proxies are often used to act as a portal through a network firewall. A proxy server accepts requests from other clients and services them either internally or by passing them (with possible translation) on to other servers. A caching proxy is a proxy server with a local cache of server responses -- some requested resources can be serviced from the cache rather than from the origin server. Some proxy servers also act as origin servers.

gateway

A proxy which services HTTP requests by translation into protocols other than HTTP. The reply sent from the remote server to the gateway is likewise translated into HTTP before being forwarded to the user agent.

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