SOCKet Secure (SOCKS) is an IETF protocol that manages multiple application sessions through a proxy server. By authenticating to a SOCKS server, a client can direct traffic to different applications beyond the server. SOCKS is often implemented to facilitate application traffic across a firewall. One important application of the SOCKS protocol is in the TOR onion router (anonymous routing) project.
See: RFC 1928.
References:
http://www.javvin.com/protocolSocks.html
http://www.networkdictionary.com/protocols/socks.php
https://gitweb.torproject.org/torspec.git?a=blob_plain;hb=HEAD;f=socks-extensions.txt