noun
summer fur; summer coat; summer plumage
Refers to the thinner, lighter coat or plumage that animals grow in warmer months. Often contrasted with 冬毛 (ふゆげ, winter coat).
猫は春になると夏毛に生え変わる。
Cats shed their winter coat and grow a summer coat in spring.
この犬種は夏毛が短い。
This breed has short summer fur.