Theoretically, a Hybrid disc could refer to:
1. A disc that contains both DVD-Video and DVD-Audio content or SACD content. (More accurately called a universal or AV DVD. The DVD-Audio standard allows this. The SACD standard does not officially allow video, so it's unclear what a given SACD player will do with a hybrid SACD+DVD-Video disc.) Other variations of this hybrid would be a disc with both DVD-Audio and SACD content, or a disc with all three formats.
2. A disc with two layers, one that can be read in DVD players and one that can be read in CD players. (More accurately called a legacy or CD-compatible disc.)
3. A disc containing one BD layer as well as two DVD layers, with a total capacity of 33.5 GB (25 GB + 8.5 GB). The disc follows the “Blu-ray Disc, Hybrid Format” specifications provided by the Blu-ray Disc Association. The disc has a blue laser along with two layers like ordinary DVD laser. The Blu-ray and DVD layers are separated by a semi-reflective film that reflects blue light while it allows the red light to pass through the DVD layer underneath.
Note: Only certain kind of drive can read both layers of a hybrid disc, and to play the hybrid disc requires a compatible player.
DVDFab offers a solution by enabling the preset as far as hybrid disc is involved: which layer is meant to be automatically recognized by DVDFab upon inverting the disc, CD, DVD, HD-DVD or Blu-ray?