Allows to move pending changes in a working git directory away and restore them later, i.e. put them on a stash. You can have multiple stashes and it can also be used to move pending changes to another branch.
If you have looked already at the Changes page of Team Explorer in Visual Studio 2019, you might have seen that it has a new Stashes section. It is shown in the screenshot below. But for what is that Stashes section?