The most common Korean word for “middle-aged woman” is 아주머니 (ajumeoni). There is one more word with a similar meaning — compare them below. 「middle-aged woman」는 한국어로 아주머니.
middle-aged woman; auntie
TOPIK 1 · noun
middle-aged woman; ajumma
TOPIK 2 · noun
Words and levels: TOPIK I essentials (National Institute of Korean Language standard curriculum, KOGL Type 1) · examples: Cheesepotato