A quick definition of Christian name:

A Christian name is a person's first name given at birth, which distinguishes them from others. It is also called a personal name. A full name includes the first name, middle name or initial, and last name. A legal name is the name recognized by the law, which can 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 surname is the family name automatically bestowed at birth, acquired by marriage, or chosen. A tradename is a name used to identify a business or product.