A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Another option that avoids the issues involved in syncing but that Msft also has made unnecessarily difficult, is to create local network locations. These allow you to open from and save to any of you sites via file explorer. The process to do this is convoluted but basically you open any Office desktop app > open > browse > enter any site address. That should open the site's libraries. While that's open, switch to this pc in explorer > right click > add network location > custom and enter the site address. Save that and it will appear in file explorer. If the connection is lost after you close explorer and try to open that site again from explorer (which it probably will be), just open it from an Office app.