QuickBooks 2013 and later allows backups to be made in Multi-user mode. This was not possible in previous versions of QuickBooks desktop.
This is how previously QuickBooks desktop normally makes a backup of a company file:
This is how QuickBooks desktop now makes backup of a company file in Multi-user mode:
Note: The full verification of a company file for backups can only be completed in single user mode and online backup can only be completed in the single user mode.