What is BBS ?

Hi,
I'm just a novice of computer. I'm using Outlook Express to read message
from "newsgroup" (OE say that is a news group) like comp.bbs.misc. Is "BBS"
is an alias of "Newsgroup". If not, what BBS is which tool should we use to
read BBS ?  (I've already know that BBS is an acronym of Bulleting Board
System).

And how about usenet ? Is it another name of BBS ?
Thanks