Recastable spell
Definition
A Recastable spell is a spell that can be re-casted even when the target is already affected by it. In such a case the spell's affect is renewed.
Examples
A level 50 aqua breath spell lasts for 1150 rounds: recasting it before it wears out will reset its duration to 1150 rounds again, avoiding any necessity of a perfect recasting timing when it wears out while you are in an underwater room.