If you are talking about the classification and meaning of the word "it" and have miscategorized your question, "it" may be a (1) pronoun or a (2) "dummy" placeholder in a sentence. (1) "It" is used as a pronoun when substituting a noun. For instance, "house" may be substituted by "it": The house was blue. It was for sale. (2) "It" is used as a "dummy" place holder in sentences with delayed Subjects or omitted Subjects. For instance, "it" placeholds for the delayed Subject "game" in: "It was a lousy game and dragged on without a score." Here, "it" placeholds for the delayed Subject "game": The game was lousy and dragged on without a score. As another instance, "it" placeholds for an omitted and implied Subject "the weight" in: "The suitcase was too heavy. It was too much for her." [Of course, in this example, some may analyze "it" as a pronoun for "suitcase"; the correct analysis depends upon the intended communication.]
If you are asking what is the meaning of Literature, as I am assuming based upon your topic and the tagging of your question, you have asked a very broad and basically undefinable question.
In the broadest sense of the word, literature is any work which is written. This would include poetry, comics, novels, interviews, short stories, even dictionaries.
In the most defined sense, which ignores many of those listed above, literature is defined by a text which provides a superior view and is designed and written in such a way that is sure to be considered merit-able far beyond the death of the author.
People define literature in many different ways- like stated in the opening paragraph "basically undefinable". While that is not meant literally, many may not agree with ones definition of what literature is given it is too broad or too defined.
For me, literature includes any text. A personal note, a poem, a song, a novel all inherently deserve to be a part of the literary category. Like finding the meaning of a poem, words are meant to be internalized and individually defined. The term literature is no different.
As for the meaning of literature, this is simply as broad as the term itself. Meaning varies in any text given readers approach each text with different morals, histories, and prior knowledge on the subject. Meaning in a text is too subjective. Even speeches (like ones given by MLK or Malcolm X) can be justified by a reader's personal feelings toward a subject.
For example, consider the Bible. Many religions interpret the text to say what 'fits' into the practicing thought of each individual membership. One could read a line from the Bible and have a very different understanding of what the text says.
Simply, meaning lies in the mind and heart of a reader.