NSCA is a Nagios addon that allows you to send passive check results from remote Linux/Unix hosts to the Nagios daemon running on the monitoring server.
It listens for host and service check results from remote machines (sent using the send_nsca program).
Upon receiving data from a remote client, the daemon will make a *very* basic attempt at validating the data it has received from the client.
If the data looks okay the daemon will make entries in the Nagios external command file telling Nagios to process the host or service check result.
