Passing
Being perceived as the gender you identify as. Passing is most commonly discussed in trans communities — a trans woman "passes" when she is read as a woman by strangers; a trans man passes when he is read as a man.
Passing is complex and deeply personal. Some trans people want to pass and find it affirming; others don't care about it; others can't pass or choose not to. Passing is not a measure of someone's "success" as a trans person.
Whether someone passes depends on many factors — hormones, surgery, clothing, voice, body language — as well as luck. For people who cannot or do not pass, being visibly trans is not a flaw. "Passing privilege" is real: people who pass face less harassment and fewer questions, but the pursuit of passing can also be emotionally exhausting.