In discussions of Magic cards, I've heard a card called a cantrip on several occasions, but I haven't been able to find a definition of what that term means for MtG. Is a cantrip a particular card, a card with a particular mechanism, or what?
A cantrip is any spell that allows you to draw a card in addition to it's regular effect (e.g. Peek). It is typically of low casting cost, and the drawing is a secondary effect.