I go by David but it's my middle name; my full name is William David Mason.
Your middle name is the name that comes between your first name and your surname. His middle name is Justin
You can use middle name in expressions such as `discretion was her middle name' and `his middle name is loyalty' to indicate that someone always behaves with a great deal of a particular quality. Geniality is my middle name. I rarely write a fierce word about any restaurant. A name that occurs between a person's first name and surname
name that is in addition to the first name used by everyone, additional name given to a baby and appears in the birth certificate; nickname which describes the person in a precise manner