Differential backups contain all changes since last full backup.
Amanda terminology
Level 0 backup is full backupLevel 1 backup contains all changes since last level 0 backup.Level 2 backup contains all changes since last level 1 backup.…Level n backup contains all changes since last level n-1 backup.
All amanda applications do not support all backup levels. Linux filesystem application (amgtar)supports backup levels 0-399. All Amanda Enterprise applications support level 0 and 1backup levels.