1. (pejorative) An exercise in tuning (see tune) in which incredible amounts of time and effort go to produce little noticeable improvement, often with the result that the code becomes incomprehensible.
2. Aimless small modification to a program, especially for some pointless goal.
3. bit bashing, especially used for the act of frobbing the device control register of a peripheral in an attempt to get it back to a known state.
