Why not det?
"Vad betyder det?" means "what does it mean?", not "what does this mean?"
Why is "vad betyder den här" not recognised as correct? Is there a rule for that?
I believe it's that if there is no specific noun being referred to, det is always used, just like in det regnar.
Is there a difference between betyder and menar?
Why is "vad betyder detta?" the correct answer here?
this is det här or detta. There's no real difference in meaning between the two; detta may be slightly more formal.
Dutch Wat betekent dit
yes why not menar?