Birth Name: This is the name you were born with, and that appears on your birth certificate. It is this name that defines much of your spiritual life, and it determines your personal Rune. A good example of a birth name is Robert Allen Zimmerman, who bears the public name of "Bob Dylan", which he made one of the most legendary names in music.
Nickname: This is the name that friends or coworkers call you by, and embodies much of your private persona. It may be a shorter form of your first name, such as "Andy" for "Andrew", or it may be completely unrelated. For example, Halle Berry goes by "Hannah" among her friends. Similarly, the man whose birth name was Samuel Langhorne Clemens, better known by his public name of Mark Twain, bore the nickname of "Sam" amongst his friends.