What is the difference between a trap and a pre-op trans girl?

Pre-op trans girls will get the 'chop' one day, identify as a girl, take female hormones, and some outright live as women.

Traps are sometimes trannies, but are also sometimes just really, really girly dudes who still identify as dudes.

Trap is slang, there's no solid definition. But when used in this context they probably mean a transvestite who just dresses up for sexual reasons, but still identifies as a male and lives as one.

A pre-op trans is just a trans who hasn't had their dick removed. "Pre" might not make sense because a lot of trans don't do that. But they could be called "traps" as well...

But you're a moron if you care about adhering to some arbitrary definition to seek approval from fucking 4chan users. If you want to live as a guy, but dress up as a girl and post pictures online, more power to you.