From the identd
Identd is a server which implements the TCP/IP proposed
standard IDENT user identification protocol as specified
in the RFC 1413 document.
identd operates by looking up specific TCP/IP connections
and returning the user name of the process owning the connection. It can optionally return other information
instead of a user name.
In other words, if you have many user
s on your computer
and one of them initiates a network socket
to a remote host
lets the remote host know which user on your system did so. This permits the remote host's sysadmin
people by username
rather than banning your whole host
if one of your user
s does something stupid
-- and, in other ways (as MrFurious
points out below) take actions on the basis of username
Why is identd important to you on a private workstation? Well, for the above reasons, many IRC servers and some FTP servers will refuse to accept a connection from you unless they can get user identification from identd on your system.