Dismissible (D)
If the duration of a spell or effect ends with “(D),” you can dismiss the effect at will as a standard action. You must be within range of the effect and be able to fulfill the same conditions required to create the effect—such as being able to concentrate to cast a spell or having access to the equipment that created the effect— though you do not actually need to spend the appropriate action. An effect that depends on concentration is dismissible by its very nature, and dismissing it does not take an action, since all you have to do to end the effect is to stop concentrating on your turn.
Source
Core Rulebook pg. 271