Having been a bit of a lurker recently I've noticed a rise in the terms, 'Doylist', and 'Watsonian' when referring to opinion based replies or to describe character thoughts, feelings and reasoning behind actions.
The most recent version of this can be found in the comments on this question here:-
The TARDIS is quite capable of making up her own mind. She's sentient, sapient, and emotionally bonded to our protagonist. She is perfectly aware of what the Doctor is leaving behind. She is giving him her support. In addition to and along with the mementos, she is also leaving behind the very same thing as the Doctor. That's as much Watsonian explanation as I need for the obvious Doylist symbolism. – Gary Botnovcan 19 hours ago
The question here being, what do these terms mean precisely?
Watsonian or in-universe commentary restricts itself to making statements that are sensible within the story's reality. Watsonian explanations are things like "Character X was lying", "He had plastic surgery over the summer", and "The main character fell off a cliff". A more precise technical term for this is intradiegetic.
Doylist or out-of-universe commentary considers the work as a created object, and prefers explanations based on the real-world motivations or circumstances of the creators. Doylist explanations are things like "The author had a better idea", "The actor died, so they had to hire a new one", and "The author got sick of writing those books, so he killed off the main character". A technical term for this is extradiegetic.
The terms reference Sherlock Holmes: Watsonian commentary relates to the in-universe author Dr. Watson, while Doylist commentary relates to the Real Life author Arthur Conan Doyle. However, they seem to have originated (or at least been popularized) on the Bujold fan mailing list.