foot-strut split

a phonemic split affecting most modern varieties of English (with the exception of most accents of Northern England and the English Midlands, along with some accents of North Wales and Ireland) in which the phoneme /ʊ/, which occurs in both foot and strut in accents without the split, is separated into two phonemes: /ʌ/ in words like strut and cut and /ʊ/ in words like foot and put.