Movement also costs action points.
A swift action is an action that may not cost an action point to use. Specifically, a hero can use one swift action for free per turn. Subsequent use of the same or any other swift action on the same turn becomes a single action.
Single action, ends turn
More precisely, most of these actions consume two action points and only end the hero's turn if no action points remain. This distinction is relevant only in certain rare cases. For instance, a hero may gain an action point after a swift-action attack (e.g. through Thornfang or a water stunt), leaving them with three action points. In this case the hero can use a turn-ending action without ending their turn.