A Microsoft file hosting and synchronization service.
Mia, I would like to add that I have NO NEED to save space on my SSD. I paid for lots of local storage for a reason. I have super fast internet, but no wish to re-live the old days when a folder needed to "load" to show the contents. With 'pinned' files, Finder still can't preview them, not to mention that the "always keep on this device" is flimsy and doesn't work.
Now I have to spend the following weeks not only fixing my own problems with this, but also explain to my wife, parents and in-laws why their "OneDrive" favourite folder is gone, why it takes forever to load a file, and then to instruct them on why these problems exist and also moving their data to a new cloud service.