Ident is the Identification Protocol, as defined in RFC 1413. It is used to ask for the username in control of a particular TCP connection on the server machine. It is often used by IRC servers to get the user names associated with connecting clients.
Ident servers usually run on TCP port 113.
l7-filter uses the ident pattern. This pattern is lightly tested. Since the protocol is so simple (the data that l7-filter looks for is a packet with only a number, a comma, and another number), it is possible that there are other protocols that it will match. However, no examples are known.