A Microsoft file hosting and synchronization service.
If you're using OneDrive, first check whether the laptop is still signed in to the same Microsoft account and that OneDrive is running. Look for the OneDrive cloud icon in the taskbar. You can also open OneDrive on the web and check if the missing files are there. If they are, the issue is likely with syncing on the laptop rather than the files themselves.
If OneDrive shows an error or says it's paused, resume syncing and give it a few minutes to update. Also check that the laptop has enough storage space.