This is the 544th most frequent Norwegian word.
flest
"Flest" means "most" in English.
Here, 'flest' is used as a superlative to indicate the highest quantity of books that he possesses in comparison to others in the class.
Han har flest bøker i klassen.
He has the most books in the class.
In this sentence, 'fleste' is part of the phrase 'de fleste', meaning 'most people', indicating a majority group.
De fleste mennesker synes at det er viktig å være ærlig.
Most people think that it is important to be honest.
Here, 'flest' is used in a comparative manner to ask about the highest number of questions one has in a group setting.