math vocabulary for tessellation:
mirror image--reflection--
symmetry--line of symmetry--point of symmetry--
translation --convex--concave angles -- rotation--
all the words that go with pattern (patterning is a math concept)--
a lot of geometry concepts, too (math connections are covered very well in
one of the Escher videos---but way over elementary kids' heads)
I am sure other list members will come up with more.