What is "wine-whine merger"

n. (context phonology English) A merger in which (IPAchar: ʍ) (the sound heard at the beginning of the word (term: whine) in a Scottish accent or several accents in the United States) becomes (IPAchar: w) (the sound heard at the beginning of the word (term: wine)); in accents where this merger occurs, (term: whine) and (term: wine) are homophones.