In an engine, the stroke is the up or down movement of the piston in the cylinder between the top and the bottom positions. One revolution of the crankshaft equals two strokes. In a four-stroke engine, each cylinder "fires" on every second revolution of the crankshaft.
Does your car really need all the maintenance services and "flushes" that your dealership or repair shop recommends? For example, what is a throttle body and why does it need to be serviced? What are the signs that your car need new spark plugs or tune-up?