The term originated from a Dungeons & Dragons slang for a spell with a minor effect.  Cantrips are included in decks for varying reasons. A cantrip can effectively "thin" a deck, so more useful cards can be drawn faster, while at the same time not losing card advantage. It can also inexpensively increase the number of spells played in a turn, which is a key factor in some decks. Some cantrips have additional effects which can serve as an answer to an obstacle in play.
Cantrips were introduced in Ice Age, where the effect read "Draw a card at the beginning of next turn's upkeep." Starting with Weatherlight, this has been shortened to "Draw a card." The Ice Age cantrips are also referred to as "slowtrips" because they are slower than drawing a card immediately.
- These cards set up a delayed triggered ability that triggers at the beginning of the upkeep of the very next turn. It doesn't matter whose turn it is.
- Mark Rosewater. (July 31, 2006.) "Cantrip Down Memory Lane", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Aaron Forsythe. (August 04, 2006.) "Magic’s Zero-Level Spells", Daily MTG, magicthegathering.com, Wizards of the Coast.
- Devin Low. (July 13, 2004.) "Ask Wizards", Daily MTG, magicthegathering.com, Wizards of the Coast.