I understand that the term was coined in 1888 by Charles Howard Hinton. He took it from the Greek words tesserais actines, which mean four rays.

A tesseract is also called a hypercube or a 4-cube. Simply put, a tesseract is to a cube what a cube is to a square.

But that’s not enough. Here’s how I received the idea.

When I was in junior high, I was exposed to a book called Flatland, by a man named Edwin Abbott Abbott. The publication date was 1884 (that must have been quite a decade) and I understand now that he intended it as a cultural satire. I didn’t read the whole book; what grabbed me was the set up and the beginning.

Flatland is just that: flat. Its inhabitants are two-dimensional shapes, and its hierarchy is based on angles; the more you have, the more you get. So a triangle is at the bottom of the social scale, and circles rule.

The flat culture experienced a mysterious event: through the plane of its existence a sphere passed. But the two-dimensional inhabitants couldn’t see a sphere – they had no depth perception – so the ET appeared first as a dot, and then as a circle which grew and grew and shrank and shrank back to a dot and nothingness. And that’s what the event was, for most of the flatlanders. But a few of them experienced a tingle of hyperperception. They couldn’t fully see or draw the sphere, but they got intimations of it.

A tesseract occupies space that has one more dimension than our own. We cannot see it or draw one. But if we relax our eyes and mind and allow the serenity of thought to proceed, we can get intimations.

Imagine that we’re sitting across from one another at a table. Between us, hovering in the air like a hologram, floats a perfect cube. Now let it blossom. Allow each of its six square faces to be one side of a new cube that extends outward from the root shape. But don’t build a cubist flower. No: the thing about a tesseract is that each of the added cubes shares its edges with its neighbors.

That’s the only way I’ve found, to peek into the universe that has one spatial dimension more than ours. And there’s no reason to assume that’s the limit. But there’s every reason to conclude that our brains, adapted as they are to three spatial dimensions, can’t reach much farther.