Zombies, mostly referred to in-universe as walkers, monsters, roamers, geeks, lurkers, biters, muertos, infected and empties, are an antagonistic force that serve as the primary catalyst for the events within The Walking Dead universe. They serve as universal antagonists.

Reanimated human beings, while not immortal, will not "die" under typical conditions that would ordinarily cause the death of a living person. They do not appear to feel or respond to pain, can survive even the most brutal injuries, and despite their bottomless appetite for flesh, they do not need food, water, or sleep to survive.

They show no other bodily function that relates to a human, showing no signs of self-healing or response to extreme temperatures. The brain maintains limited abilities of the body, allowing for movement of the limbs (provided that they are not decomposed to the point where the bones are not strong enough to bend without breaking), jaws, neck, and even the use of its sensory systems. While the walkers are notoriously weaker than humans, the only way to kill one is to destroy the brain. Despite severely weakened frames, they will continue to hunt for living animals to consume. Even when decapitated, the head will remain active, even though it would be practically harmless at such point.

All the info you might need: https://walkingdead.fandom.com/wiki/Zombies 

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Time Commitment: 2 Years, 4 Months (28 Volumes) 

That time commitment figure is actually just the maximum amount of time you might be working. Zombies are played by multiple people (any gender) and a new person to play zombies is cast every month. Essentially, you can stay with the project for a long or little as you like. 

Every month, one more person will be cast and added to the group of zombie voice actors, so if you audition for zombies previously and weren't cast, be sure to re-record/resubmit your audition this month (to show that you're still interested and active.)

Zombies have sound written out in text form pretty specifically in the comics. Your job is to match the essence of what those words are trying to convey as exact as you can, while still sounding like a roaming, compulsion-driven zombie.

Not all the sounds are coming from the same zombie. The zombies' voices COULD vary in pitch and maybe in texture. Have fun with this one and try different things!