The word "zombie" is never used. The zombies are either referred to as "Walkers", "Geeks", "Skanks", and to the CDC, "Test Subjects". In season 2 the terms "Roamers", "Lurkers", and to Hershel, "People", and "Lame Brains" are added. In season 3 "Biters" was introduced to the lexicon.
In an online interview, it was revealed that Frank Darabont envisioned having several self-contained episodes that would not continue the main story. One such episode would have been the season two premiere. It would have involved Sam Witwer (who Darabont used in The Mist (2007) and played the tank zombie in the series premiere) as a solider in a Black Hawk Down (2001) style Atlanta. Witwer would have encountered several of the cast before being bit and locking himself in the tank.