This is the 326th most frequent Persian word.
زیاد
"زیاد" means "too much" or "a lot" in English.
Here, 'زیاد' is used as an adverb to indicate the frequency or quantity of the action (reading books).
من زیاد کتاب میخوانم.
I read a lot of books.
In this context, 'زیاد' is used as an adjective to describe the abundance of food.
غذا در این رستوران زیاد است.
There is a lot of food in this restaurant.
Here, 'زیاد' is again used as an adverb, but in a negative form, to show the lack of intensity of the action (studying).