cloudHQ sync pair defines the following:
1) what to sync (i.e., which folders to sync, which cloud accounts to sync, etc.) and
2) how to sync (i.e., one-way sync, backup sync, sync for migration, two-way sync, how to convert documents, etc.).

Backup mode copies data in one direction, from the source to the target. It keeps older versions of your files (a file is archived before it is changed or deleted) and overwrites the target to match the source.

Migration mode also copies data in one direction. It copies the sharing information of your files and folders as well, and the option to archive files before they are changed or deleted is turned off.

Also please read the definition of sync.