The open-mid central unrounded vowel is a type of vowel sound, used in some spokenlanguages. The symbol in the International Phonetic Alphabet that represents this sound is ɜ, and the equivalent X-SAMPA symbol is 3. Note that the IPA symbol is not the number "3", but a reversed epsilon.
Thomas, Erik R. (2001), An acoustic analysis of vowel variation in New World English, Publication of the American Dialect Society, vol. 85, Duke University Press for the American Dialect Society, ISSN0002-8207