Exile

Exile is a concept introduced in Menagerie. Each player gets one Exile mat if there are any cards that use them in the kingdom. To exile a card is to place it on the Exile mat, where it is out of your deck (but still in your possession), temporarily. When you gain a card that has any copies on the Exile mat, you may discard all copies on the mat.

List of cards that use Exile

There are eight cards that use the Exile mat and six landscapes
Stockpile
Bounty Hunter
Coven