A Microsoft file hosting and synchronization service.
Thank you, John!
But OneDrive Personal issue: all Word/Excel/PowerPoint files disappeared at once. I did NOT delete them.
Files previously appeared in Home/Recent but opening them said "Item does not exist". Recycle Bin is empty. Storage is now under 0.1 GB. After signing in again, all recent files disappeared.
I need a human support agent to check OneDrive backend/account state or recovery options.