This is the 3968th most frequent Swedish word.
mestadels
Mostly; mainly; for the most part.
In this sentence, 'mestadels' means 'mostly', indicating the frequent activity that the person performs in the evenings, which is reading books.
Jag läser mestadels böcker på kvällarna.
I mostly read books in the evenings.
Here, 'mestadels' is used to describe the usual state of the weather during summer as being sunny most of the time.
Vädret här är mestadels soligt på sommaren.
The weather here is mostly sunny during the summer.
In this example, 'mestadels' is used as an adverb to qualify the overall quality of the food, indicating that for the most part it was good.