Schwa is the name given by linguists to /ə/, 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 schwa is easily confused with IPA: /ɜː/, the 'open-mid central un- [or slightly]-rounded vowel' - both are produced very centrally in the mouth, and both are very relaxed.
The symbol for a schwa in the IPA is /ə/. (The word schwa is of course also used as a name for this symbol, which printers call a 'turned e', ə.)
Schwa is pronounced very like 'shah' with a '-w-' inserted, IPA: /ƒwɑː/.
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 'sulphur').
- Etymological note: The word schwa is almost a transliteration of the Biblical Hebrew שְׁוָא (shewa), the name of a sign, consisting of two dots one above the other, which is placed underneath a consonant to indicate that, in pronunciation, the consonant is to be followed either by a short ‘e’ sound or by no vowel sound at all. The Hebrew word שְׁוָא (shewa) comes from a root meaning ‘nothingness’.