What is the definition of the modern zombie? The definition that we use at the Zombie Research Society is that the modern zombie is a relentlessly aggressive reanimated human corpse driven by a biological infection. You can break that down into three parts.
The first one, relentlessly aggressive: You're not going to negotiate with a zombie; you're not going to talk a zombie out of wanting to eat you. You're not going to say, "Hey, zombie. Eat my friend instead of me. I'll give you $100 if you don't eat me. Eat that family around the corner; you get 5 for 1." A zombie will continue to do what it wants to do until it is physically unable. It doesn't matter if you chop its legs off, it will still try to eat you. It doesn't matter if you threaten it, it doesn't matter if you bribe it, it will continue to try to eat you.
Second, reanimated human corpse, self explanatory: A dead human who stands back up and starts walking around, and trying to find you and eat you. Third is the most important part of the definition, a biological infection. What that means is that zombieism, the zombie sickness, is biologically-based. It's not based on some ancient superstition or myth. It's not caused by a curse. It's an infectious disease much like any other infectious disease that we have, just a lot worse. Zombies can spread their sickness through biological means. If you get bitten by a zombie, you turn into a zombie. It's one of the things that makes zombies unique to almost all other monsters, that they are biologically-based.