The two-stroke cycle of an internal combustion engine differs from the more common four-stroke cycle by having only two strokes (linear movements of the piston) instead of four, although the same four operations (intake, compression, power, exhaust) still occur. Thus, there is a power stroke per piston for every engine revolution, instead of every second revolution. Two-stroke engines can be arranged to start and run in either direction.
Animations, explanations, and diagrams of labeled parts of two-stroke engines can be found at How Stuff Works.
