So called “branded slots” are slot machines featuring a brand name owned by someone else than the game developer.
Typically, the owner of the brand will require a license fee for the use of their brand. This will usually mean a lower Return To Player (RTP). The game developer doesn’t want to lower their profit margin to pay for the license fee, and neither does the casino operator. The option that is left is lowering the RTP. This is why so called branded slots normally have a lower RTP.
This issue doesn’t pertain just to slots based on movies or TV-series; the third-party brand used can just as well be something else, e.g. a branded board game, a pop group, a sporting event, or a computer game character.
Examples of branded slots include: South park, Lord of the rings, Jurassic Park, Games of thrones, Monty Python, Terminator, The creature of the black lagoon, The dark knight, Iron Man, Electra, Fantastic Four, Transformers, the battle for cybertron and many more.