Term used by Sigmund Freud and now in psychological and general use meaning the desire for sex. Originally, Freud thought libido was an actual, physical energy, similar to Kundalini, and that blockages to the energy resulted in psychological problems. On a practical level, however, he could not encourage his patients to seek sexual encounters. So he changed the concept of libido from energy to a desire.
Since blockages in the energy could cause problems, Freud needed something that would block or counter libido as a desire. He called this the Death Wish.