Open-mid central unrounded vowel
The open-mid central unrounded vowel, or low-mid central unrounded vowel, is a type of vowel sound, used in some spoken languages. The symbol in the International Phonetic Alphabet that represents this sound is ⟨ɜ⟩ (formerly ⟨ᴈ⟩).
Source: Wikipedia — Open-mid central unrounded vowel (CC BY-SA 4.0)