It is called an acronym.
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".
This technique is called an acrostic. An acrostic poem or description uses the first letter of each line or word to spell out a name or phrase, often providing characteristics or qualities associated with that name. It's a creative way to highlight someone's traits using the letters of their name.
Sylvester Stallone
Engraver
Vandal
Lev Tolstoy (was a Russian novelist)