Coated, fully-coated, multicoated, fully-multicoated optics. Why are these important?
Optical coatings reduce internal light loss and glare and ensure even light transmission, resulting in greater image sharpness and contrast. Spotting scopes have numerous glass surfaces, each one contributing to scattered light, so coatings make a big difference in what you see. Coated optics will have a less shiny, even dark appearance when looking into the barrel or tube. You may see a greenish, bluish or brownish tint as well. Most coatings are magnesium fluoride or calcium fluoride and work by destructively interfering with certain colors or wavelengths of light, eliminating their reflection. More light gets into your scope and more light is able to pass through to your eyes. Almost all modern consumer optics have some kind of coating on most of the optical elements. However, there are different levels and qualities of coatings.
Coated optics means that at least one of the major optical elements has a coating on at least one surface. Fully-coated means that all lenses and glass surfaces have a coating layer. Multicoated means that at least one of the major optical elements in a fully-coated scope has multiple coatings of antireflective compounds on at least one surface. Fully-multicoated means all glass surfaces have multiple coatings and it is the best kind, resulting in light transmission of 90-95 percent, bright, sharp and contrasty images.