Vaults are places where you can directly upload files/folders from anywhere to youraccount, with a simple drag-drop for those files/folders. You can also copy any of your backed up files/folders to the Vaults for sharing purposes.
There are two type of Vaults: Instant Vault and Cold Vault.
If you you are aBusiness user, you can have the both types of Vaults added to youraccount.
If you you are aHome user, you can only have Instant Vaults added to youraccount.
For more information about how to add/enable Vaults, please check out this article.