Trap
Trap is a subtype for Instants introduced in Zendikar, and also featured in Worldwake.[1][2]
Description
Traps may be cast as for their regular mana cost, but also have an alternative cost should specific events occur. Usually traps have abilities that undo whatever has made their alternative cost possible, e.g. a Trap that was enabled by two lands entering the Battlefield under an opponents control destroys two lands.
Examples
Trivia
The card Pitfall Trap was based on the artifact Pit Trap[3]