Groupings of programs which allow you to have different playback settings (jump amounts, timestretch etc) per groups of shows.
Group membership can be set manually, before or after recordings have taken place or by regex.
To define playback groups, go to Utilities/Setup > Setup > TV Settings > Playback Groups.
To change a recordings playback group, select a recording in the Watch Recordings screen. Press I for info and select Recording Schedule > Edit Recording Schedule > Storage Options and change the Use "Default" playback group to the desired group.