2 Movement actions

Immediate Action
Trigger: Each immediate action—usually a power—defines its specific trigger. The one type of immediate action that every combatant can take is a readied action.

Once per Round: You can take only one immediate action per round, either an immediate interrupt or an immediate reaction. If you take an immediate action, you can’t take another one until the start of your next turn, but you can’t take an immediate action on your own turn.

Interrupt: An immediate interrupt lets you jump in when a certain trigger condition arises, acting before the trigger resolves. If an interrupt invalidates a triggering action, that action is lost. For example, an enemy makes a melee attack against you, but you use a power that lets you shift away as an immediate interrupt. If your enemy can no longer reach you, the enemy’s attack action is lost.

Reaction: An immediate reaction lets you act in response to a trigger. The triggering action, event, or condition occurs and is completely resolved before you take your reaction, except that you can interrupt a creature’s movement. If a creature triggers your immediate reaction while moving (by coming into range, for example), you take your action before the creature finishes moving but after it has moved at least 1 square.