DriverSide's Car Dictionary has the most comprehensive definitions of automotive terms. This auto glossary can help you decipher what your mechanic is fixing and what the purpose or function of the particular auto part or accessory is for. We have taken the mystery out of automotive service jargon, so that you don't have to.
The piston moves up and down in the cylinder (unless you've got a flat "boxer" engine, in which case it moves horizontally) to compress the air/fuel mixture, which is then sparked by the--you guessed it, spark plug. The timing of that spark is critical; too soon or too late, and things stop working correctly, and in some cases bending and breaking.