Comprehensive Rules (408.2)

To retire a card is to put it from play into its owner’s discard pile. Players can only retire cards they control, and only cards in play can be retired. Retiring a card is not the same as dismissing it.

Comprehensive Rules (408.2)
To retire a card is to put it from play into its owner’s discard pile. Players can only retire cards they control, and only cards in play can be retired. Retiring a card is not the same as dismissing it.