When we call a man a Casanova, we mean he has had many sexual relationships with women — not one partner, but a long line of them. The word is a person’s name that turned into a type. Giacomo Casanova was a writer from Venice in the 1700s. He became famous for his many love affairs, and for writing them down. Today if someone says “He’s a real Casanova,” they often smile, but it is not always kind: it can mean he is charming and good at winning women, or that he does not stay and treats love like a game. It sounds a little old. Younger people may say player instead. We almost always use it of a man, not a woman. Many writers keep a capital C, because it started as a name, though a small c turns up too. It is not a job, and it is more than “he likes to flirt” — the real point is many sexual relationships, though people sometimes stretch it just to mean a big flirt.