Faking a swim

I recently read an article or comment on SwimSwam where someone mentioned the term 'faking a swim'. As I understand it, it usually implies a swimmer swims and trains for events X and Y well but, due to previous training history, natural ability, or effects from training for events X & Y they can put up a respectable time in event Z. I've heard it before but would be interested in hearing others thoughts on what qualifies as faking a swim, what enables a swimmer to do so etc... Not looking for insight on how to personally accomplish one.