Nat is a slang term from the Wild Cards novels referring to normal humans uninfected by the Wild Card virus. Most often used by Jokers when referring to their uninfected oppressors, though also occasionally employed by Aces as a pejorative. Fleur van Rensselaer (daughter of the ace Brain Trust) once observed that, though the term is short for "natural," it has another secondary meaning as a homonym - "gnats," which reveals how some wild carders feel about non powered humans. Nat is one of the few words in the parlance of Wild Cards that does not have its origin in card game terminology. It is unknown who first coined the word.
Ironically, some nats might actually be infected with either the recessive or latent form of the virus and not know it. Recessive carriers inherited a portion of the virus, attached to their DNA, from one of their two parents. In this form the virus will only manifest in children conceived with another recessive carrier. When latent, the carrier is infected with the full blown virus. They appear normal, but the virus could activate at any time and due to any of a number of triggers, high stress levels being the most common.
Latent carriers come in two kinds: Some have been infected by a cache of the original spores released into the atmosphere on Wild Card Day. Others inherited the virus from both parents, but in a dormant state. This second variety is something of a rarity since the trauma of childbirth usually causes a newborn to "turn their card." The most famous of this kind of carrier was John Fortune, who did not manifest any wild card powers/symptoms until his thirteenth birthday.
Another unique latent carrier is Dr. Tachyon, who was infected by a communicable form of the Wild Card spread by Croyd Crenson.