alpha; A, α +

(Greek: ; beginning, first of anything; first letter of the Greek alphabet; used in physics and chemistry to designate a variety of series or values)

phonetic alphabet (s) (noun), phonetic alphabets (pl)
A set of symbols, each representing a distinct speech sound: In her book, Linda read about the phonetic alphabet as a standardized set of characters or signs used in phonetic transcription.

You can see all of the letters of the Greek Alphabet on this page.