Near your starting location in each of the five Acts, you will find a large chest -- your private Stash. It is a secure, permanent, SAFE place to store any precious items and gold you find in your adventures. Use your Stash to hold any items you intend to keep but do not want occupying space in your Inventory. Items left on the ground will disappear after a few minutes.
You are the only one who can access your Stash. Another player cannot look inside or access your Stash for any reason.
The items in your Stash are saved during the game and when you exit the game. You only have to worry about losing items in your Stash when you die in Hardcore Mode. You can learn more about Hardcore Mode here.