Passing
Being read as your gender without your trans history showing — and a contested goal.
Passing means strangers read you as your gender and think nothing further. For many trans people it's tied directly to safety: passing reliably means fewer confrontations and less daily negotiation.
The word is also criticised, and fairly. It implies a test administered by other people, with cis appearance as the pass mark, and it makes an involuntary thing sound like an achievement. Some prefer being read correctly, which puts the emphasis where it belongs.
Whether someone passes varies by context, lighting, clothing and the observer, and it shifts through transition in ways nobody controls.
A trans person who doesn't pass is no less their gender. Passing describes what strangers perceive, and strangers are not the authority on anyone's identity.