As it says in the manual, and I strongly suggest that you read that as there is some further explanation: NOP is a dummy instruction that has no effect. It can be useful as the target of a THEN or ELSE clause.
cheers enrico When I tell somebody to RTFM or STFW I usually have the page open in another tab/window of my browser, so that I am sure that the information requested can be reached with a very small effort