In the Walking Dead universe, the word "zombie" doesn't exist. Prior to the outbreak of the virus, the universe didn't have any zombie-based films or media. There are many words and phrases used to describe the undead in the show, but some of the most common are walkers, roamers, lurkers, biters and infected. The most common "walker," was first used by Morgan Jones. Rick adopted the term and brought it to the Atlanta group of survivors.