Tessering, a significant part of the fiction of A Wrinkle in Time, is a mode of travel in the fifth dimension that utilizes the shortest route. It can be used in space and in time. When used in space, it combines the straight line of the first dimension, the square of the second dimension, the cube of the third dimension, and the Einsteinian space-time continuum of the fourth dimension to create a circular space across what Einstein called the "fabric" of space-time. This circuitous fifth dimension works equally across space and time. This concept, called a tesseract, and the concept of traveling by tessering, are illustrated when Mrs. Whatsit has Mrs. who fold the fabric of her skirt to allow a wrinkle in space (the fabric) to provide a short commute for a bug from one location to another across the wrinkle.
Charles said, ... "Well the fifth dimension's a tesseract. You add that to the other four dimensions and you can travel through space without having to go the long way around. ... [in terms of] Euclid, or old-fashioned plane geometry, a straight line is not the shortest distance between two points."
Meg tries to understand tessering and the tesseract but is not able to grasp the full meaning of the things she is told, though the illustration using Mrs. Who's skirt of the wrinkle shortening space travel is clear and comprehensible. Then Charles tries to explain it for her and for a glimmer of a moment she can see its meaning:
"I see it!" she cried. " I got it! For just a moment I got it!I can't possibly exp-lain it now, but there for a second I saw it!"
Nonetheless, Meg still bases her understanding of knowledge upon rational thought, and a fifth dimension that enfolds all other dimensions is somehow still out of her notion of rationality. When the Happy Medium asks her to name other darkness fighters, she names Euclid and Copernicus--two of the most rational of men, both mathematicians and one an astronomer:
"Oh, Euclid, I suppose." Meg was in an agony of impatience ... "And Copernicus."