The stash, represented by a chest in towns and outposts, is a repository where characters can store items in a safe, central location. The contents of the stash are the same regardless of which town the stash is accessed from, so characters do not need to move items from one area of the game world to another.
The stash is shared between all characters on an account that also share the same league. Each league will have its own stash, inaccessible by characters outside the league.
When a temporary league ends, contents of the stash from that temporary league will be moved to the parent league. If there is not enough room in the parent league's stash to accommodate all the items from the temporary league, additional "read only" pages are created in the parent league's stash to hold the extra items. Extra stash pages created in this way cannot have items placed in them, they can only have items removed. After all items have been removed from the extra pages, they disappear.