Frap is to
masturbate. It is the word Americans should be using after they stopped using jerking off so much and started using the quite erroneous fap. They are unlikely to do this however as they seem to have a lot of
trouble spelling many English words.
Frapping was originally the way in which a rope is tied to some logs or oil drums, for example, to make a raft in watermanship.
Frapping was first used to mean masturbation on a British
army assault pioneer course circa 1991. I know I was there.