1) Will never know the true chill of death, but will never know the fiery passion of life again
2) An undead being who hungers for MAN FLESH
3) A sickly, shambling entity that has rotting flesh stripping off his body
4) A being who knows only one word: "AUUHHHHHHHHHHH"
However you define it, you will know a zombie when you see one.
Above is a specimen of a 'fresh' zombie, one who has not yet reached the 3rd or 4th stage of decomposition. Zombies are usually in various forms of decay, especially if the Virus theory is applied. For an example...
Above is a specimen of an extreme case - the zombie has no flesh whatsoever.
All zombies should be targetted, and destroyed.