For many, the issue of a deadname can come up with government organizations or internet accounts, as in Facebook's infamous "real name" policy.
More About Deadname
While referring to someone by their deadname (their birth name or terminated name) is problematic, in the case of trans individuals whose changed name is typically reflective of their gender, using a deadname (or "deadnaming") is particularly disrespectful as it effectively mis-genders them. To avoid this, it is always best to refer to anyone by the name they ask you to use.