Libido is someone’s desire to have sex — the drive itself, not a person and not a describing word. Doctors and psychologists use it. Freud made it famous, and in his writing it sometimes meant a wider life energy, not only sex. Though actually, when ordinary people say libido now, they almost always mean sex drive: a high libido, a low libido, her libido came back after she rested. It is a somewhat formal, doctor’s-office word. Friends might say sex drive instead. You do not usually count it (not “three libidos”), but you will hear a high libido or a low libido. It was borrowed from Latin libīdō, “lust, desire,” and first used a lot in psychology. It has nothing to do with liberty or with library, even though it starts the same way.