A Ph.d is a doctorate. A person with the letters Ph.d after their name is called a Doctor, even if they did not study medicine.
A person who does not believe in god is called a "Athiest"
Letters that stand for parts of a name are called initials.
Using all capital letters for a name is called "acronym."
Marie Antoinette
Spell out your name vertically on a piece of paper. Think of traits that describe you that start with certain letters of your name, until all the letters have a trait connected to them.
An acronym or abbreviation. When it is a name, then it is called that person's "Initials", as in "E.B White".
Engraver
Vandal
Sylvester Stallone
Lev Tolstoy (was a Russian novelist)
Lev Tolstoy (was a Russian novelist)