Nhadala

The original use was a 4chan gag showcases feminine looking characters or transsexual people as a joke about how you wouldn't know they had a penis until you got them in bed

Then it evolved (from my understanding fairly quickly) to be a general term for anime characters that appear female but were actually male

The main thing here is that anime has very, very few representations of actual transgender individuals, meaning that this usage is almost universally used without referring to trans people

pretty sure snare traps outdate 4chan