Each recording or re-recording is another generation of video and/or audio material. The loss of generations is due to the degradation caused by successive recordings.
The newly recorded material is the first generation, a re-recording of the same material would be the second, etc.
This loss concerns, above all, the analog editions and to a lesser extent the editions with digital equipment, although the digital VTRs are also subject to Drop that increase the more a tape is played.