Deadnaming
The use, whether intentional or not, of a trans person’s birth name, instead of their chosen name (if they have one). Using a trans person’s old name is offensive, a form of misgendering, and can cause trauma, stress, embarrassment, and gender dysphoria. It is seen as disrespectful of the person, and by extension, all transgender people.
Note: Not all trans people use the word “deadnaming,” as it can imply that a trans person dies when they transition. “Birth name” is a preferred alternative.