Annie Perkins, a teacher in the Twin Cities, defines math art as something which inspires curiosity about structure. If you are looking for activities to teach your students math through the making of beautiful art, check out her Math Art Challenges.
Explore Celtic Knots, Sona drawings, probability designs, Islamic Geometry, Hitomezashi stitching, Hilbert curves, Mondrian puzzles, spirals, and more. Some are advanced, but most are accessible to all.
A good place to get started is to scroll through the Math Art Challenge page linked above. Annie included a picture of each project in the list, so it's easier to find one to try. You can also browse the #mathartchallenge hashtag on Twitter to see what others have done.