The term "tranny-trap" is a slang term used in the adult industry, specifically in the context of transgender or transsexual porn videos. It is derived from two terms: "tranny", which is short for transgender, and "trap," which refers to someone who is attractive but might not be immediately identifiable as transgender.
The phrase "tranny-trap" is often used in the context of describing a video where a transgender performer may initially appear as a cisgender man or woman, but later reveals their trans status. The term implies that the person is attractive and potentially deceptive in terms of gender identity, which can be intriguing to some viewers.
Please note that this term is considered offensive by many transgender individuals and should only be used when describing adult content and not for any other purpose.