Uniform Resource Locators
Uniform resource locators-more commonly known as URLs-are used as the primary naming and addressing method of the Web. URLs belong to the larger class of uniform resource identifiers; both identify resources, but URLs include specific host details that allow connection to a server that holds the resource.
A URL can be broken into three basic parts: the protocol identifier; the host and service identifier; and a resource identifier, a path with optional parameters and an optional query that identifies the resource. The following example shows a URL that identifies an HTTP resource:
http://host_domain_name:8080/absolute_path?query
The HTTP standard doesn't place any limit on the length of a URL, however, some older browsers and proxy servers do. The structure of a URL is formally described by RFC-2396: Uniform Resource Identifiers (URI): Generic Syntax.