The schwa is a mid central vowel that is very common in English. In English it is mainly found in unstressed positions, but in other languages it also occurs frequently in stressed positions. The term was introduced into linguistics by Jacob Grimm in the early 19th century.
The English schwa does not correspond to a single letter. Notice that it is represented by different letters in the following words:
Some speakers produce a high front unrounded vowel instead of a schwa in certain words. For example, some speakers use the high front vowel of sit in words such as chicken, needed and boxes. In British English, the names Lennon and Lenin contrast. The first is produced with a schwa and the second with a high front vowel. In American English both names are usually pronounced with a schwa. In both varieties of English, however, roses and Rosa's are distinguished. The first word has a schwa and the second has the vowel of but.
The schwa is a very common vowel in English. It is a short vowel that usually occurs in unstressed syllables. It is so common that it can correspond to a number of letters.