This is the 589th most frequent Czech word.
většina
"Většina" means "majority" in English.
Here, "většina" means "most" or "the majority," referring to the greater part of a group (people in this case) expressing agreement.
Většina lidí souhlasí s tímto názorem.
Most people agree with this opinion.
In this context, "většina" specifies the larger portion of a collection (books in this sentence) and describes their quality.
Většina těchto knih je velice zajímavá.
Most of these books are very interesting.
The word "většina" here again stands for "most" or "the majority," this time applied to students who succeeded in passing the exam.