SRV (service) records are used by some network protocols to provide service-specific aliasing and load-balancing. For example, XMPP (Jabber) uses SRV records to locate the XMPP server for a domain; rather than connecting directly to "example.com" or assuming a specific server hostname like "xmpp.example.com", an XMPP client would look up the "xmpp-client" SRV record for "example.com", and then connect to whatever host was pointed to by that record.
Undocumented in source.