A trap is a term referring to an anime character who represents themselves both emotionally and physically as a different
gender than they actually are. This can be said for any gender but it is most commonly used to describe a male character who dresses and is represented in a very feminine
way. Even to the extreme where people in that show or the audience may
mistake or assume the character to be a woman, only until its is specifically revealed to be wrong. Some people in the
anime community have found this term to be offensive or even transphobic since the term is mostly used in a negative light. It is also easy for people to accuse characters of being traps, even if the a character is only doing something minor such as crossdressing, which most of the
time does not fit the term since you are already known up front that they are not the gender they are presented as. So make sure when your using the phase it fits this
definition!