1. The distance between the center terminal ( electrode ) and the outer terminal ( electrode ) through which the spark must travel in a spark plug . Also see spark plug gap and air gap .
2. The distance between the points in contact breaker points . See point gap .
3. The distance between two vehicles travelling down the road as they go in the same direction. Generally a safe distance is a minimum of two seconds behind the vehicle in front.
4. The distance between the two ends of piston rings . See piston ring end gap .