Parallax
A change in apparent position of an object/subject relative to more distant objects, caused by a change in the observer's line of sight towards the object/subject.
Example:
Cover one eye and focus on an object. Then change eyes and focus on the same object. The object will appear to move.
Literary Parallax
The connection between the writer and the reader, and the ability the writer has to almost 'control' the perspective the reader has. This is can be done by instructing the reader to carry out instructions, or changing perspectives between paragraphs and stanzas. From telling readers to read something first, to changing from the perspective of a young girl to an old man - the writer can control the direction of which the reader's thoughts are stirred and potentially alter their view point on the story or medium used.
Example:
"Think really hard as you read this. Please concentrate and give your full attention.
Now, I want you to look at the first line of this passage. Yes, the line you just read. Reread it. Study it. Try to pull out something out of it that you hadn’t before.
Now, think about what you just did. You probably looked at the first line of this passage. Probably. You didn’t have to. It won’t add anything to your comprehension of this work. But if you did look back at the first line, I have a question for you: When did you go back to read it? Was it after the first command? Or after you read the entirety of the second paragraph? Or in between “Reread it” and “Study it”?
This is not a conventional way of writing and I intend for you to feel differently as you read this. I write for some imaginary person in the future, and you read the words of some bygone writer – we don’t usually think in these terms. We don’t really reflect on the inherent dynamic playing out between us. I can write anything that I want you to see and you have no control. By the same token, you can think anything you want to and I have no control. It’s quite a marvel that any progress is made through the creation of written works.
The purpose of this passage is for you to contemplate the relationship between writer and reader. I do not know if I have succeeded, but I hope I did. This is a very difficult idea for me to convey due to my inexperience as a writer and the implicit complexity of this topic. But think about how the beginning of this passage made you act. Some elegantly designed ink on plain paper or perfectly positioned pixels on a computer screen commanded you. And you (probably) listened."
From --> http://sequelmagazine.org/literary-parallax/