What is an "Optical Mode". I've been reading a lot of solar cell articles, especially those having to do with nanophotonics. There is a term that I keep running into, 'optical mode', but I've yet to find an explanation that I can visualize or understand. What exactly is the "mode" being used here? I know it ha to due with confining light to a certain area withing a optical waveguide, but I'm not sure what a mode is. Can someone explain in layman's terms what it is?