Tessellation is about filling a flat space with multiple copies of congruent shapes in
a repeating geometric pattern.
A regular tessellation is made up of identical regular polygons.
A semi-regular tessellation is made up of two or more different kinds of regular polygons.
And an irregular tessellation is made up of congruent irregular polygons, or even other
shapes.
I’m not going to say much more about tessellations, except to point out that in my opinion, some
of the most fascinating tessellations I’ve ever seen were drawn by M. C. Escher. Go look
him up.