In hip hop, moving a record back and forth on a turntable in a rhythmic fashion. Performed by djs, the first scratching on wax was probably either Herbie Hancock's "Rock it," or an early song by GrandMaster Flash whose title escapes me at the moment. It was the one in which Fab Five Freddie was given a shout out. Flash is usually regarded as the inventor of the technique, whether or not he was the first to do it on a record.