The Japanese name, "Jūnishishi", is a play on the terms "Jūnishi" (十二支), which refers to the twelve signs of the Chinese zodiac, and "Shishi" (獣), meaning "beast". The English name, "Zoodiac", is a portmanteau of the words "zoo" and "zodiac".
The "Zoodiac" monsters are based on the Twelve Animals of the Chinese Zodiac, with each monster being a slightly anthropomorphized version of their respective animal. Each monster also wears an oversized gauntlet on either their left or right forearm, with which they wield their own respective weapon.
The "Zoodiac" monsters in the Main Deck possess effects that allow Beast-Warrior-Type Xyz Monsters they are attached to to gain different effects, ranging from Spell/Trap negation to piercing damage.
The Xyz Monsters of the archetype, meanwhile, all possess variable (?) ATK and DEF, stemming from the sum total of the ATK and DEF of the monsters attached to it as Xyz Material. Furthermore, each Xyz Monster can be Xyz Summoned once every turn by using a different "Zoodiac" monster as the Xyz Material.
The basic premise of the archetype is to stack up as many members as possible as Xyz Materials for their Xyz Monsters, making them gain more ATK/DEF and additional effects for each material they manage to gather.
The archetype is extremely reliant on "Ratpier" as its primary play maker meaning if you were to prevent the opponent from being able to play it through cards such as "Prohibition", the archetype would be unable to do much of anything. Also, many of its combos require the use of 3 "Ratpiers", meaning if you were to banish 1 the archetype would be greatly hindered until they can return it to the deck. It does a lot of special summoning, meaning cards like "Maxx "C"" and "Vanity's Emptiness" can hinder this deck. Also, while it has good recovery, speed, and consistency, the archetype lacks raw power and therefore is reliant on other archetypes, such as "Kaijus" or "Metalfoes", to do the bulk of the heavy lifting.
Zoodiac is a very combo-oriented deck, and as such can be difficult to master. An explanation of a few of the core combos can be found here: