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 and has fewer moving parts. Two-stroke engines are commonly used in small machinery, such as chainsaws and lawnmowers, due to their high power-to-weight ratio. In a two-stroke engine, the combustion process occurs every revolution, which results in more power output for the same engine size. However, they are generally less fuel-efficient and produce more emissions than their four-stroke counterparts. The use of a fuel-oil mixture is also necessary for lubrication, which can contribute to environmental concerns related to pollution.