Zen is the name of the virtual currency used throughout Perfect World Entertainment's games. Zen is used to purchase items in the game's cash shop to enhance the user's experience. Zen can be purchased with real-life money or doing Peanut Labs surveys. Zen can allow you to buy many things in Blacklight: Retribution, including special equipment, gear, weapons, camo, aesthetic modifications, and much, much more. Zen is also a source of controversy in the community, and this controversy is known as "Pay To Win" taking into account the game's Free To Play model.
ZEN compared to GPEdit
Game Points, which are awarded for playing matches, can also be used to buy most items. However, you must meet the level requirement for the item you want to buy. If you purchase an item with ZEN, this minimum level will not apply, you can immediately use the item regardless of your level. All basic weapon types are permanently buyable with GP. So while a player using ZEN can cut short the time until he owns a specific item, a player who relies on GP is not excluded from owning it, too. However, there are some items that can only be purchased with ZEN, like Premade Weapons, Camo, Reward Helmets (indirectly through chance packs) or Heroes. While premade weapons and heroes may give an advantage on the battlefield, it is possible to "bootleg" their weapons and equipment with Game Points and enough time invested to reach the unlock level. It should be noted that neither ZEN nor GP can be used to buy special ("elemental") Ammunition permanently (though it can come with a Premade). Most of the items that can only be bought with ZEN would classify as 'cosmetic improvement' and won't allow a player to become overpowered.