A
reverse-trap is a heterosexual (usually) female character who dresses like, looks like or pretends to be a boy and 'passes' to the extent that NO ONE other than perceptively intelligent characters or complete degenerates (skirt-chasers) recognize them based on 'bone structure', 'having suspicions' or 'always knowing'. These characters are often outed at some point in the story through various means.
These characters also tend to focus on the 'I'm not that pretty trope' where they find themselves unattractive and another character (usually a male) who likes them or is close to them reassures them they are very pretty/beautiful/sexy ect... although not all reverse-traps have or
exibit this trope like, Zelda in her
Sheik form (Ocrina of Time),
Pidge (Voltron 2018),
Samus (
Meteroid Prime) or
Sypha (Castlevania).
Trans-men are NOT considered reverse-traps although, tomboys can technically be a possible reverse-trap depending on the portrayal.