person who does a very convincing job of passing
as the opposite sex (ie. a crossdresser).
According to Knowyourmeme, the word was coined in the early 2000's from the meme "IT'S A TRAP"; it was, and still is, primarily used by anime and video game communities to refer to effeminate male characters, such as Bridget from Guilty Gear, who look so feminine as to fool fans into thinking that they are actually women.
However, "trap" has drawn criticism from the trans community, with many insisting that it is (or in some cases, always was) intended as a slur towards trans people (ironically, the trans community originally co-opted the word for themselves, likely before realizing the connotations it carried). While calling a trans person a trap does reflect a mindset that gets trans people abused or killed, it should be noted that a word being considered derogatory in one context does not make it derogatory in all other contexts.
Person 1: "Bruh, Hideri is best trap"
Person 2: "Uuummmm tr*p is a transphobic SLUR that reflects a mentality that gets trans people KILLED, and I will report you for hate speech
if you use it again"
Person 1: "But I was talking about a crossdresser
, not a tran-"
Person 2: "NOPE, NOPE, STOP TALKING, GO TO JAIL"