Most spells are cast instantly and their effect is worked out at once. For instance, the Fire Ball spell is cast, it strikes a target and damage is resolved. In this case, the spell has no further effect in the game during the same Magic phase, and the spell cannot be cast again in that Magic phase.

Some spells last for longer than this and they are said to Remain in Play or Last One Turn. These spells cannot be cast again while they remain in play.