A cantrip is a slang term used to refer to a spell that draws a card in addition to its other effects (usually minor) and can therefore be said to replace itself.  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.