Source : Free On-Line Dictionary of Computing

no-op
     
        /noh'op/ alt. NOP /nop/ [no operation] 1. A machine
        instruction that does nothing (sometimes used in
        assembler-level programming as filler for data or patch areas,
        or to overwrite code to be removed in binaries).  See also
        {JFCL}.
     
        2. A person who contributes nothing to a project, or has
        nothing going on upstairs, or both.  As in "He's a no-op."
     
        3. Any operation or sequence of operations with no effect,
        such as circling the block without finding a parking space, or
        putting money into a vending machine and having it fall
        immediately into the coin-return box, or asking someone for
        help and being told to go away.  "Oh, well, that was a no-op."
        Hot-and-sour soup that is insufficiently either is "no-op
        soup"; so is wonton soup if everybody else is having
        hot-and-sour.
     
        [{Jargon File}]
     
        (1994-12-02)