A level even lower than a "beta" individual, a Zeta is someone who allows Alphas and Chads to bully and order him around, being too scared to act out against them.
"Bro, do you see that Zeta kid Eric over there? Let's go make him put away our trays and carry our shit."
"Look out for "Zetas" on twitter.com. They're open zoophiles who advocate for humans having sex with animals. Somehow they aren't banned yet. Insanity."