This is the 142nd most frequent Persian word.
بسیاری
"بسیاری" means "many" or "a lot" in English.
Here, 'بسیاری' is used to express a large quantity of a specified group, in this case, 'books'.
بسیاری از کتابها در این کتابخانه بسیار قدیمی هستند.
Many of the books in this library are very old.
In this sentence, 'بسیاری' is used to indicate that the subject interacted with a significant number of specified places.
او بسیاری از مکانهای دیدنی شهر را بازدید کرده است.
He/She has visited many of the city’s attractions.
The word 'بسیاری' is employed here to reference an unspecified, general group of people agreeing on a statement.