argument of send()

[Pter0dactyl]

send(socket_name,sending_buffer,size_of_buffer,0);

can someone tell me about the fourth parameter of the send() and recv() functions.I want to know the use of it.

[kbw]

http://pubs.opengroup.org/onlinepubs/007908799/xns/send.html

http://en.wikipedia.org/wiki/Out-of-band