A surname is a name that is passed down from a person's parents and is part of their family name. Sometimes people have two surnames instead of just one, and this is called a double surname.
When someone has a double surname, it means they have two last names instead of just one. For example, instead of just being called "Johnson," they might be called "Johnson-Smith." This happens when a person's parents both have surnames they want to pass down to their children.
In some cultures, having a double surname is a common tradition. In other places, it's not as common but still allowed. Sometimes people choose to have a double surname even if it's not a tradition or common practice.
Having a double surname can make it a bit more complicated when filling out forms or giving your name to people. But it can also be a way for someone to honor both sides of their family and their unique heritage.