This is the compression codec used to shrink the movie file size while trying to keep the picture clear.
This is the "red flag" in the name. It indicates this isn't an official digital release. "PreDVD" usually means it’s a high-quality recording of a cinema screen (a "cam") or a leaked early screener.
Because it’s a "Pre" release, the audio is often muffled, the colors might look washed out, and you won’t get the high-frame-rate (HFR) or HDR experience that James Cameron intended for Pandora.