Deadnaming

Deadnaming is using a name (called a "deadname") that a transgender person used before transitioning without their permission. It is called that because the person who that name belongs to is considered "dead" and is now a brand-new person. 
Sometimes, people deadname another person by accident. They may know the other person before they transitioned. Other times, people deadname other people on purpose. Using a person's deadname is considered to be very disrespectful because it ignores a person's gender identity and is a type of transphobia if it happens on purpose. Some people think that deadnaming is a form of violence.
Obstacles.
It is very hard for people to change their names on forms because there is a lot of paperwork involved. That means that they are more likely to experience deadnaming.