Runner- These are the newly turned. They haven't lost any muscle yet so they're fast, not as fast as an Olympic athlete, but they can run you down because they don't feel the pain of pushing themselves.
Walker- These are the ones who have been turned for quite some time. It usually takes a few hours for their bodies to become stiff and start losing muscle so they can only walk/ stumble like the typical zombie in the movies.
Crawler- These are zombies that have lost the use of 1 or both of their legs or even had their entire lower half removed ie. being ripped apart.
Burner- This is a zombie that has been lit of fire that will eventually become non-threatening due to their brains and brain stem being burned to the point that it can no longer survive.
Pet- a pet is a walker that has had it's arms and jaw removed like in the Walking Dead. Usually they would be someone's loved one that they can bare to destroy so they remove their arms and jaw to keep them around.
Swimmer- Swimmers are zombies that have made their way into water and can't get out. Given enough time, their bodies will soak up the water like a sponge so they'll appear extremely obese and slimy.
Duster- Dusters are zombies who were once burners but didn't burn them self's to new death. Their brain stems still continue to function, however their bones, flesh and muscles are extremely brittle and no effort would be needed to re-kill one.
Roller- This would be a handicapped person who's been turned.
Young Dead- This is a child who's been turned.
Infant Dead- This is a baby or toddler who's been turned.
TD- "TD" stands for Teen UN-Dead or Dead Teen.
ED- This stands for Elderly undead
TT- or Twin Terrors are 2 zombies moving together.
Triple- 3 zombies moving together.
Pack- a group of 5-10 zombies.
Horde- a group of 11 or more zombies.
Psy- Siamese twin zombies.
Beast- a beast is an animal that's been turned or bitten. Most animals that have been turned will act as if they have rabies.
(There are other "Beast" classifications that are the same as above you just add beast after the term ie. "Runner Beast", "Burner Beast" etc.) Head- No this isn't the tip of a male organ (perverts). A "Head" is literally just that... it's a decapitated zombie head that's somehow still alive.
Potential- This is someone who's been bitten or scratched but hasn't developed the symptoms just yet.
Turner- This is someone who's been bitten or scratched that hasn't yet turned but is experiencing the fever and hallucinations.
Fresh- someone who's recently been killed or died but hasn't yet turned.
Impaled- These are zombies that have been caught in traps ie. hung or stuck on stakes or under cars. They're still a threat but stuck.
Frosty- These are zombies who were caught by winter and have either slowed way down or have been frozen stiff until the temperature rises. They are still a threat.
Armed- These are zombies who probably lost a limb in life and had it replaced by a hook etc before they turned.
Thinkers- These are zombies who've shown the ability to adapt and think such as developing a trap for survivors or being able to get through places they shouldn't be able too.