The state or process of acting or doing: The medical team went into action. Something done or accomplished; a deed. See Usage Note at act. Organized activity to accomplish an objective: a problem requiring drastic action. The causation of change by the exertion of power or a natural process: the action of waves on a beach; the action of a drug on blood pressure. A movement or a series of movements, as of an actor. Manner of movement: a horse with fine action. Habitual or vigorous activity; energy: a woman of action. Behavior or conduct. Often used in the plural. The operating parts of a mechanism. The manner in which such parts operate. The manner in which a musical instrument can be played; playability: a piano with quick action. The series of events and episodes that form the plot of a story or play. The appearance of animation of a figure in painting or sculpture. Law A judicial proceeding whose purpose is to obtain relief at the hands of a court. Armed encounter; combat: missing in action. An engagement between troops or ships: fought a rear-guard action. The most important or exciting work or activity in a specific field or area: always heads for where the action is.