- The definition of a screw up is a mistake or something that has been done in error.
An example of a screw-up is a streaky, messy, blotchy paint job that has to be totally redone.
- To screw up is to make a mistake or error.
An example of screw up is when you add 2+2 and accidentally come up with 5.
- a serious mistake; blunder; mess
- a person who screws up
- (idiomatic, colloquial) Alternative spelling of screwup.