Feel free to correct me if I'm wrong, but I'm pretty sure a Trap is just a boy/man dressed up like a girl/woman. Whereas Trans people actually feel like they were born the wrong gender. Now, if you mean Trans as in Transvestite, then I'm not sure what the difference would be between Trap and Transvestite. I know Transvestites get sexual gratification through dressing up in women's clothes, I'm not sure if the same could be said of Traps. Maybe Traps are just trying to 'ensnare' boys/men into sleeping with them? I don't know.
Also, futa and trans should be 2 different tags. Trans people can be in transition and have boobs and a penis, but that doesn't make them futas. A futa is a hermaphrodite with both completely formed male and female genitalia and that doesn't happen in nature. Yes hermaphrodites are real, but they don't have fully formed genitalia, just characteristics of both. Like a clit that is long enough to look like a small penis or something along those lines.