Thank you for at least not being a prick about how your time is too valuable to spend explaining.

As for those examples, I'd class them a bit differently, not even similar to each other. Movie was a new word for a new thing. I wouldn't class that as slang so much as naming something that didn't have a name. Motion picture isn't a name, it's a descriptive phrase standing in the place of one.

TV, on the other hand, I would class as abbreviation, basically an initialism. It's closer, but I wouldn't say the OECD was a slang term. Slang has at least the distinction of not being the 'official' name of a thing. 'Pie' cannot be slang for 'pie.'

Telly, on some other hand I'll have to borrow, I would probably class as slang, but just a piece that entered the common lexicon. It's so ubiquitous that I don't expect there's any way to tell who first coined it, but you could make a pretty safe bet it was some clever dick who made the choice to not use the established word for the thing, either putting the cognitive load on the listener rather than bear even the tiny load of just saying the word, or being intentionally obscurant to feel clever. I don't know what you would call someone who puts a load on others to make their own life better, but it wouldn't be 'nice.'