Trap
From Fan History Wiki
Trap is a commonly used term on the 4chan boards, and refers to a character (usually male) who appears as a member of the opposite gender. A female character dressed as a man/boy is a reverse trap.
The popular meme of Admiral Ackbar saying "It's a trap!" (from Star Wars) is often applied to these characters. The TV Tropes Wiki summarizes this meme:
Many Wholesome Crossdressers in anime are drawn really, really pretty, to the point where they can be passed off as actual female characters to new fans with surprising ease. The Four Chan fanbase itself modified an old quote-turned-meme to describe this kind of a character as a "trap", in the sense that a highly stereotypical, undersexed, and loudly heterosexual male otaku would be trapped in a conflicting lust for the character. At this point, the jargon is used ironically.[1]
