This starts drifting way off topic, but hacks are typically characterized by being "clever". Which is hard to define, but is usually surprising in some way. I

This starts drifting way off topic, but hacks are typically characterized by being "clever". Which is hard to define, but is usually surprising in some way. I think it stops being a hack when the surprise is gone - when you've explored the mechanism, understand the tradeoffs, where it does make sense and doesn't, etc.