"Natty" means natural, and describes those who lift without performance enhancing drugs such as steroids, although some questionable supplements might be allowed. The opposite, describing those who use such drugs, might be "enhanced".
What's the questionable supplements allowed? Herbal stuff like ashwagandha or whatever, or not-technically-steroids-but-close-enough substances like SARMs?
Creatine is common among people who've maxed out their beginner gains but who are still chasing PRs. You get a fair bit of it naturally in food, and it's been studied to death by nearly every sports medicine program in the world: https://my.clevelandclinic.org/health/treatments/17674-creat...
Creatine will let you push an 8 rep set to 9 or 10. And when every pound on the bar is bought with two weeks of complicated periodization, that little bit helps. And creatine is allowed by basically every athletic league.
Real PEDs are a whole different ball game. Much bigger risks.
I think most people would count anything not forbidden for Olympic athletes as natty (not that most Olympic athletes actually are, but that's another discussion).
Yes. Bodybuilding (big muscles and low body fat, for aesthetics) is very much a place where chemical assistance is common. But there are those who prefer to do it natural (and are way less likely to die young).