Definition: Boxer engines are two-cylinder powerplants with horizontally-opposed cylinders, and the name derives from the fact that the pistons move in an outward "punching" motion, and the cylinder heads protrude on either side of the bike. BMW motorcycles are among the best known manufacturers-- especially with their so-called older "airhead" powerplants-- for their boxer engine configurations.
Examples:
That old boxer engine looks like it shields the rider's shins from the cold.
