A stroke is the full single action of an engine to intake, compress, combust, and finally to exhaust a fuel. This action is typical of a 4-stroke engine. The combined action of intake, compression, combustion, exhaust, causes the shaft of the engine to spin. This action is repeated at a rate referred to as rpm's, revolutions per minute. The way "rpm's" are measured varies by the type of motor, and what "stroke" that motor is.