This question already has an answer here:
Words like 大人、下手、上手... as おとな, へた, じょうず.
What is the name for terms of this type?
Kanji that don't use their specified readings.
The answers for おみやげ don't answer the classification of non-standard pronunciation (they answer other questions but the stated one).
The おとな related question is very specific to that word.
I believe the other stated duplicate doesn't answer this in general either. It would very hard for a searcher to find these somewhat duplicate questions.