why jquery is called as library, insted of framework
Well, the folks over at jQuery refer to jQuery as a library which is a very good indication that jQuery is a library.
jQuery is a fast, small, and feature-rich JavaScript library. It makes things like HTML document traversal and manipulation, event handling, animation, and Ajax much simpler with an easy-to-use API that works across a multitude of browsers. With a combination of versatility and extensibility, jQuery has changed the way that millions of people write JavaScript.
A library is code that you get to add to an application which makes programming easier. You - as a programmer - do not have to reinvent the wheel. A Framework is much larger environment that let's you build an entire application and contains many libraries.
A quick Google search explains the differences between a library and a framework..
https://stackoverflow.com/questions/148747/what-is-the-difference-between-a-framework-and-a-library