In English it is the neutral vowel that typically occurs in weakly stressed syllables, e.g. the final syllable in sofa and the first syllable of above.

The IPA symbol for schwa
The IPA symbol for schwa

Etymology -
The name derives from the Hebrew sheva, which denotes a Hebrew diacritic that is placed under a consonant to show that following vowel sound is absent.

Oxford English Dictionary -
Its first citation is from 1895:
"‘schwa’ or the neutral vowel."
(P. Giles Compar. Philol. 134 Indo-G.)

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