Also, a concept used in the popular Sci-Fi children's book by Madeleine L'Engle A Wrinkle in Time. The tesseract is a concept used to explain time travel in the sense that a line is the shortest way to travel between two points
O--------O
However, if you can imagine placing your finger in the middle of that line, and folding the line so that the two endpoints are
side by side, then you can see how the line is technically not the shortest way, but rather to
fold it. The book used the example of an ant crossing this distance as it would travel between two points on the hem of a skirt.