Depots Chests are storage in the game where you can keep items in a safe place while you are not using them.
The Depot Chest is a box located in a Locker along with an Inbox and Market access. Multiple lockers can be found in a Depot building.
While there are only 17 slots in the Depot Chest more items can be stored in Depot Boxes and Containers that you can put in every box. The maximum amount of items that can be held in all depot boxes together is 2,000 items for free account players, and 10,000 items for premium account players. See this tip for storage ideas.