Zombies are mindless creatures animated corpses usually controlled by their creator. Evil Wizards or Priests are the only known species that can animate and bring a corpse back to life. Whatever condition the corpse is in at the time of its death is the same as when it is animated. If the corpse was missing a limb, once returning in its zombie state, it will still be missing that limb.
Zombies move very slowly, attacking anything that gets in their way, what they leave in their wake is horrifying. Dismembered and half eaten bodies are left strewn across their path. Zombies will always fight unless called off by their creator or until they are destroyed. Destroying a zombie is not always difficult, a shot to the head or fire will usually destroy them completely.
Zombies have an unyielding stench of decay that can alert victims well in advance that they are coming. And due to their slow movement, it is difficult for them to catch you if you run. However, most zombies are formed in groups, or "pacts," making it more difficult for anyone to escape. They encircle an area and the touch of one can freeze you in place it is so cold.
Some zombies can attack with weapons though it is uncommon. It can be difficult for even the most powerful Wizard to find fresh bodies to turn into Zombies, so the mass majority would be in rather sorry shape, and easily escaped from.