Definitions for "Differential backup"
A differential backup backs up only transaction logs, but does not clear them. If you perform a full backup and then perform only differential backups, the last full backup plus the latest differential backup has all data needed to bring the database back to the most recent state. This type of backup is also called a cumulative incremental backup.
Differential backup allows users to copy files created or changed since the last full or incremental backup. It does not mark files as having been backed up. If you are performing a combination of full and differential backups...
a backup done only of what have changed since a previous backup (the "backup of reference")