Screen Lock

I am just wondering how we lock the screen in OS X. Is there such feature is OS X like in windows where we can lock the screen and unlock it with alt + ctrl + del? Perhaps the closer one to this featere will be fast user switching in OS X, but it's not the one that i really want.

http://www.mac-forums.com/forums/showthread.php?t=44899&highlight=Screen+Lock
http://www.mac-forums.com/forums/showthread.php?t=37791&highlight=Screen+Lock
http://www.mac-forums.com/forums/showthread.php?t=37316&highlight=Screen+Lock

Oh cheers for the references. I've been inactive for quite a while that i didnt know that so many discussions about this