It can be used as substitute for the word retard or calling someone gay. It is basically an insult that people don't understand, so it can be used in almost any situation without offending someone.

n. The birth name of somebody who has changed their name. Most commonly attributed to trans people, but can be attributed to any person who has changed their name. (sometimes written as two words: dead name)

v. 1. To call somebody by their deadname.
v. 2. To out somebody's deadname to the public.