An address, usually for locating Web pages. (e.g., FTP//:abc.org). The part before the first colon specifies the access scheme or protocol. Commonly implemented schemes include FTP, HTTP (World-Wide Web), gopher or WAIS. The "file" scheme should only be used to refer to a file on the same host. Other less commonly used schemes include news, telnet or mailto (e-mail). The part after the colon is interpreted according to the access scheme. In general, two slashes after the colon introduce a hostname (host:port is also valid, or for FTP user:passwd@host or user@host). The port number is usually omitted and defaults to the standard port for the scheme, e.g. port 80 for HTTP.