Other forms: libidos
Libido is a person's sexual desire. Once a year? Once a week? Once a day? There is no correct answer, because everyone's libido is different. However, you hope your partner's is similar to yours!
Libido has only been a word for about 100 years, though the urge to have sex has been around, well, as long as we have. It is Latin for “desire, lust.” You may have heard that the libido changes over the course of a person's life, and that you can even "lose" it if you are, for example, depressed or taking certain medications. People often think famous psychoanalyst Sigmund Freud coined the term. It isn't true, though he did popularize it in his writings on sexual urges.