So a few episodes exist in isolation. Films are the obvious example of episodes that stand-alone (although I guess franchises like The Godfather or Star Wars or Home Alone could be grouped together). And occasionally (fairly often on Radio 4) there are single episode documentaries or dramas which are not grouped into a wider series. And at the risk of repetition PIPs v3 (unlike v1/2) allows episodes to be orphans with no parent brand or series).

More commonly episodes are not orphaned and are grouped by a brand or a series (which may in turn be grouped by a brand or a series). At this point it all gets a bit complicated. An episode may be an orphan. Or it might belong to a series. Or it might belong to a brand. And a series might belong to another series. Or might belong to a brand. Or might be an orphan. And a brand is always an orphan.