A rude word for feces, falling between shit and dookie, to be used as a noun (I stepped in crap), verb (I crapped in a hole), exclamation (Oh Crap!) or adjective (thats crappy). The name does not come from the inverter of the modern toilet, whose name was Thomas Crapper. Instead, it comes from the middle english "crappe" which was the grain that was walked all over in a barn. I'm told by walter that in England one might say "that movie was a bit crap". Them silly Brits.
Thanks to ctf for pointing out that Tom Crapper wasn't the of the originator of the word, and the correct origin.
I got some info from http://www.wordorigins.org/wordorc.htm#crap