eli5: in music, since there are 12 notes per octave, why are only 7 letters used instead of 12?

Question

eli5: in music, since there are 12 notes per octave, why are only 7 letters used instead of 12?

In: 15

Answer 1

Using a guitar sting as an example.

E, F, F#, G, G#, A, A#, B, C, C#, D, D#, E

I used sharps because I don’t know the symbol for flat on a keyboard.