When an animal molts, it drops an old covering and grows a new one. Birds molt feathers; snakes and some insects crawl out of an old skin; some dogs and cats molt fur in a heavy season. You can use it as a verb (the parrot molted) or as a noun for the time or the process (during molt). This is the American spelling; British English writes moult. You will meet it in nature writing, farming, and talk about pets — not a rare lab word. People sometimes joke that they are molting when their hair falls out, but that is playful stretch, not the core use. Though actually, the word grew out of old forms of melt: the idea was of something coming apart, like melting away, and later it settled on this shedding sense. Do not mix it with melt. Ice melts; a bird molts.