What is an exposition?

I've actually not much clue whether what my idea of exposition is correct. Anyways, here I go:

It is a writing or speech primarily intended to convey information or to explain. It is a good way to put across an arugment and convince the reader or listener about the author's view on a certain topic. Usually, I guess, a good exposition contains two sides of the issue. 

In an online dictionary, I found the following meaning for exposition:

1.a setting forth of the meaning or purpose (as of a writing)2. discourse or an example of it designed to convey information or explain what is difficult to understand
I think very much sums up what's an exposition. We all use exposition very often, I think, even the essays we write for SS and History are expositions!