Question

how do you define literature?

Answer 1

books or writings are wrote with some particular subject that is called its literature

Answer 2

Literature can be defined as artistically written works or literary texts. 
Literature can also be termed as reports or writings on a particular subject. 

Usage of literature in a sentence-
My favorite subject in school is French Literature.
We read 'The Road Not Taken' by Robert Frost in our Literature class.

As you can see by the above sentences, literature is a noun.