In Terry Pratchett's Discworld novels, the undead are seen less as monsters, and more as characters with unusual cultural quirks. They even have their own bar in Ankh-Morpork.
The term "undead" is used on the Discworld to refer to many races that seem to be more like separate species, such as werewolves, banshees and bogeymen. Zombies are the only race that belong exclusively to the category "undead", in that they were once living (and human, in all cases seen so far). Vampires are borderline, in that some used to be human, whereas most seem to have been born as vampires.
Zombies are one of the basic kind of undead. Essentially, they are people who are dead, but haven't stopped moving. The zombie activist Reg Shoe makes a distinction between 'proper' zombies and mere 'old memories on legs', describing the former as aware and goal-oriented. Unlike zombies in most folklore and horror fiction, they are not automatically mindless, but may retain the same personality they did when they were alive.