The primary focus of Meep is simulating the interaction of light with Photonic Crystals (periodic materials that control light based on both their shape and composition).
You may have heard of optical metamaterials (aka "invisibility cloaks"). They are sometimes made with photonic crystals, but photonic crystals aren't always considered metamaterials. Butterfly wing coloring is a good example.
http://en.wikipedia.org/wiki/Photonic_crystal
http://ab-initio.mit.edu/wiki/index.php/Meep_Tutorial/Band_d...
You may have heard of optical metamaterials (aka "invisibility cloaks"). They are sometimes made with photonic crystals, but photonic crystals aren't always considered metamaterials. Butterfly wing coloring is a good example.