A quick definition of first name:

A first name is the name given to a person at birth, which distinguishes them from others. It is also known as a personal name or given name. A person's full name includes their first name, middle name or initial (if any), and surname. A legal name is the name recognized by law, which may be acquired at birth or through a court order. A nickname is a name given to a person as a term of endearment or familiarity. A tradename is a name used to identify a business or product.