Explain the meaning of LISTEN socket primitive

The listen Primitive:

After identifying a protocol port a server should instruct the operating system to place a socket in passive mode therefore this can be used to wait for contact from clients. To do same a server calls the listen procedure that takes to arguments:

listen( socket , queuesize)

Argument socket is the descriptor of a socket which has been created and bound to a local address and argument queue size identifies a length for the socket's request queue.