SRV record (A Service record) is a specification of data in the DNS defining the location, i.e. the hostname and port number, of servers for specified services. It is defined in RFC 2782, and its type code is 33.
Some Internet protocols such as the Session Initiation Protocol (SIP) and the Extensible Messaging and Presence Protocol (XMPP) often require SRV support by network elements.
Source: http://en.wikipedia.org/wiki/SRV_record
