WHAT?
I usually explain better in person, but let's try in text...
If you lived in a one dimensional world. Everything would be a point, and either in front or behind you. There's no left or right, just forward and backward. The whole world would be a line, and nothing more.
Now imagine a two dimensional world, there's forward, back, left and right, but no up and down. Everything you see or perceive is either a line or a dot, no curves, no third dimension. The world would be like flatland, as [MENTION=171297]snap[/MENTION] pointed to.
Now imagine yourself as a 2 dimensional being, and take the following example:
On paper, draw a right-angle triangle ABC where AB = 3cm BC = 4cm, so whats the shortest distance between point A and C in two dimensional space? SqRoot of 3^2 + 4^2? = sqrt of 9+16 = sqrt of 25 = 5 cm?
Now think like a 3 dimensional being interacting with the 2 dimensional paper. Whats the shortest distance in your 3 dimensional world between A and C?
Zero
How?
Fold the paper so that A and C touch.
However, if you were a 2 dimensional being, living on the 2 dimensional paper, the shortest distance would still be 5 cm, and you wouldn't be able to perceive the folding across the 3rd dimension. If anything, you would see some matter or energy from point A appear in point C – magically.
Say, the distances weren't cm but light years, and you observed light from point A reached point C almost instantaneously. Thus, light was travelling faster than the speed of light, and your whole world would seem upside down! Laws of physics of your 2 dimensional world were being broken and you would wonder at things such as dark energy or try and find explanations such as higher dimensions...
The fact that the universe expanded (matter moved) at faster than the speed of light perhaps hints at more dimensions than we can perceive in our 4 dimensional world (space-time is 4 dimensional).
I hope that made some sense