1. An animal used for meat and for milk. Domesticated. Sadly, this animal has had a rather bloody history, and not even their babies are safe from being turned into food; the little ones become an evil food known as veal.
2. A term for a nasty, stupid, and/or promiscuous person (usually female), despite that cows are cute and relatively intelligent animals.
I'd call Ann Coulter an ignorant cow, but that would be insulting to the cow; cows (and dogs) are too cute and too smart to be seen as horrible; she's a fly.