It's a simplified explanation of the geometric concept of "tiling the plane" where shapes are placed, like flooring tiles, onto a 2D surface, a plane. In this case I think pattern is just the layman's terms being used for simplicity's sake because, when you look at the assembled tiles, it's the same shape repeated (but not the same repeated configuration of several of these shapes, which is what makes this novel).

https://en.wikipedia.org/wiki/Tessellation