Courtesy of Curiosity.com:
“You live in a three-dimensional world, one where you’re free to move forward and backward, right and left, and up and down. You’re also familiar with lower dimensions: a drawing on a page is two-dimensional, for example, and a line could be considered one dimension. But what about a world with four dimensions? We can describe it with numbers, but as a concept, it’s pretty hard to picture. That’s just the challenge that Edwin Abbott Abbott took on in his 1884 novella “Flatland.” It’s about the difficulties in describing higher dimensions to beings in lower dimensions, with a sizable helping of political and social commentary to boot.
The narrator of the story is a square, a well-to-do mathematician with a line for a wife and four pentagon sons. (In this society, the more sides you have, the higher your status. All of the women are lines.) He lives in Flatland, a two-dimensional world where shapes move north/south and east/west, but have no concept of up/down.