It refers to back up all the data on the selected folders, partitions or hard disks, whether it has been backed up or not. That is to say, full backup always back up all data on the selected target places. Moreover, a full backup is the basis of incremental and differential backup. If you have had a full backup before, then you can employ the following two methods-Incremental and Differential Backup modes to save time in backing up.
You can still directly start an full backup for a backup image from the Backup and recovery page by clicking Backup --> Full backup.