What's a woot?

I suppose it's quite normal for the Facebook Generation to use some old words that shock the old folks and invent some new ones to confound us. There's a strange word that one sees all over the social network world these days.  It is apparently an exclamation, usually to express great pleasure.  This is the only time I will ever type it and I refuse to say it. That's good because the Facebookers would get a good laugh upon hearing a geezer use their word.  Woot!