A two-stroke engine is a type of internal combustion engine that completes a power cycle in just two strokes of the piston, or one crankshaft revolution. This design allows for a simpler and lighter engine compared to a four-stroke engine, as it does not require valves. Instead, it uses ports for the intake and exhaust of gases, making it more efficient in certain applications. These engines are commonly found in small machinery, such as lawn mowers, chainsaws, and some motorcycles. They are known for their high power-to-weight ratio and ability to operate at high RPMs. However, they tend to produce more emissions and consume more fuel than their four-stroke counterparts.