Col is the main form of currency in AoA (Age of Aincrad). Players have access to sell and purchase items from NPC merchants; trade with other players using it, or buy items through player-made shops. One thing that makes the Col system interesting is that players can also use Col during quests to persuade NPCs into doing things such as letting them through a border, helping them with a task, etc.
When a player receives Col, it adds to their virtual funds, known as a “Col Counter”. This system is incredibly simple, and is best explained like this: Col is essentially an item in the player’s inventory, but does not take up inventory space.