Schwa
For a note on how AWE organizes its group of articles on vowels, basically by aspects of sound and of writing, see category:vowels.
This is the name given by linguists to the commonest vowel sound in English - the unstressed weak vowel heard in the usual native pronunciation of 'the', in natural; speech; to students of phonetics, the 'mid-central vowel'. If you want to hear it, say 'The President of the United States' as naturally as you can. You should hear a schwa in the middle of this - in both 'the's.
The symbol for a schwa in the IPA is /É™/. (The word schwa is of course also the name of this symbol - a 'turned e', É™.)
schwa is pronounced very like 'shah' with a '-w-' inserted, IPA: /ʃwÉ‘Ë/.
The schwa can be represented in writing, in the normal English alphabet, by all five of the regular vowels: a (as in 'usual', 'burglar'), e ('the'', adviser' and 'centre'), o ('pastoral' and 'doctor') and u ('occur' and 'harbour').