What is Literature?

From the V Century, men has being trying to answer the definition of literature. The Greeks started this process, but even nowadays, we don't have a clear denomination of the word. Some people think that literature is every single piece of written language, but others define it as something of pieces of "high culture", that means, Shakespeare's novels, poems, etc. 
In our Course Companion book, they define literature as "A highly developed use of language in that is the stylized manipulation of language for larger effect (purpose) and/or affect (emotional response)". So, from now and on, I'll use this definition of literature, that would include only highly developed pieces of written language and no magazines, cooking books, etc.