PvP is the main playstyle of Zombie Survival and was the original concept before PvE. In PvP, all players are put against other players, with a small amount of players (around 16%) being forced onto the Zombie team at the start of the round. When a Zombie kills a human, the human is then moved onto the Zombie team and becomes yet another Zombie (in contrast to PvE where any humans who are killed will be moved to spectator).
PvP can be played with up to 32 players, and is intended for large groups of players.
PvP, unlike PvE, focuses on the masses and the entirety of gameplay, rather than on a few individual players and close teamwork. Maps on PvP are often larger and roaming is intended.