A nymphomaniac is a woman that people say has nymphomania: they mean she wants sex often, usually with a lot of different men. You can also use it as an adjective (a nymphomaniac character in a film). It is nymphomania plus -ac — the same kind of ending as in maniac. In real life the word is often unkind. People use it to joke, to gossip, or to put a woman down. It is not a careful doctor’s label anymore. A woman who likes sex, or who has many partners, is not automatically ill, and this word does not prove anything about her health. You will meet it in older books and in messy everyday talk; handle it as a loaded word, not as a fact.