Spaces like this (manifolds) are usually classified by which Euclidean space they look like locally. So, for example, the surface of a sphere is two-dimensional since it locally looks like a plane (whence flat-earthers). A two-dimensional torus can be visualized as the surface of a doughnut, but also as a square where going off an edge brings you to the opposite edge.

As explained in the article, the torus in question is locally three-dimensional, and you might mistake it for ordinary 3d space at first. The specific geometry we're visualizing is the 3d analogue of the square from above: it's a cube where going off an face brings you to the opposite face.