Synchronization vs. Backup / Mirroring / Replication
Synchronization, Backup, Mirroring and Replication are all methods of copying files between 2 or more locations / folders.
Synchronization potentially copies files in either direction, while Backup, Mirroring and Replication always copy files in one direction (a.k.a. \'pushing files\').
ViceVersa uses the modification timestamp of files to determine which files are newer. All methods copy only those files that are different. This means that repeating a backup will not copy any files, if no files have changed.