A double name means that a person has two names instead of just one. This happens when parents combine two names to create a new name for their child. For example, if a mommy and daddy named Sarah and John decide to give their child a double name, they might choose the name Sarah-John or John-Sarah.
Having a double name means that people will address you by both your names, and sometimes they might even choose to use just one of your names. It's important to remember that having a double name is just an option and not everyone has one.