schwa/shwa  (n.)

The usual name for the NEUTRAL VOWEL , heard in English at the beginning of such WORDS as ago, amaze, or in the middle of afterwards; sometimes called the indefinite vowel. It is a particularly frequent vowel in English, as it is the one most commonly heard when a STRESSED vowel becomes unstressed, e.g. telegraph becoming telegraphy . It is also the usual pronunciation of the vowel in such words as the, a, an, and. The term ‘schwa’ comes from the German name of a vowel of this CENTRAL quality found in Hebrew.