Specifically the wife of
叔叔 (father's younger brother). Chinese kinship is precise:
伯母 (wife of father's elder brother),
婶 /
婶婶 /
婶子 (wife of father's younger brother),
舅妈 (wife of mother's brother),
姑妈 (father's sister) - all 'aunt' in English. Also used as a friendly form of address (
李婶 'Aunt Li') for any older neighbor woman.