What is a spark plug gap?

Answer 1

"Spark plugs are typically designed to have a spark gap which can be adjusted by the technician installing the spark plug, by the simple mechanism of bending the ground electrode slightly to bring it closer to or further from the center electrode. The belief that plugs are properly gapped as delivered in their box from the factory is only partially true, as proved by the fact that the same plug may be specified for several different engines, requiring a different gap for each. It can depend on the engine: new spark plugs might be pre-gapped for a V-8 engine, installing all 8 plugs unchanged; however, for a 6-cylinder engine, all (6) plugs would be re-gapped." strait from wikipedia. http://en.wikipedia.org/wiki/Spark_plug