It’s called mildew. “In places with stagnant air, such as basements, moulds can produce a strong musty odour.” [0] - https://en.m.wikipedia.org/wiki/Mildew ht

It’s called mildew. “In places with stagnant air, such as basements, moulds can produce a strong musty odour.” [0] - https://en.m.wikipedia.org/wiki/Mildew https://en.m.wikipedia.org/wiki/Mildew