A tessellation is a series of repeated identical shapes that fill in a given space without any gaps. Artist M.C. Escher is a famous creator of tessellations; his celebrated works of tessellated birds and lizards are some of the best-known examples of this combination of art and math.
Tessellations can be complex images with interlocking shapes of flying birds, crashing waves or swimming fish. They can also be simple creations, such as equal-sized squares lined up in rows with no gaps between them. Another word for tessellation is "tiling," which makes sense considering how neatly arranged and identical tiles can be.