A creature is a thing that can be engaged in meaningful interactions due to its mental capacity, in contrast to objects and space. The birds in the trees, the barmaid serving dinner, the red dragon attacking the countryside, the skeletons guarding a long forgotten treasure, and your player character are all examples of creatures.
Powers that target a number of creatures can target you, your allies, and your enemies up to the number specified.[PH:57]
Creatures are classified into the following groups based on general appearance and behavior:[MV:5-6]
Creature Size: how much space it occupies
Creature Origin: which plane it came from or has strong ties to
Creature Type: what its basic shape and behavior is like
Creature Keywords: some additional information like race, elemental alignment
Level: how powerful it is relatively to other creatures
Role: how it functions an encounter either whether character or monster