to call a a transgender person (= a person whose gender does not match the body they were born with) or non-binary person (= a person who has a gender that is not male or female) by the name that they no longer use because it matched the gender they were said to have at birth

Why does the media insist on deadnaming trans people? 为什么媒体一再用跨性别者变性前的名字称呼他们？

He was upset at having been deadnamed all over the Internet. 他因为互联网上到处都在用自己的弃名错称而感到很受伤。

When a person is deadnamed, it not only outs them but can also put them in a potentially dangerous situation.