These categories break down generally how you would expect: ID flooring is designed for indoor areas with minimal-to-no water exposure, while EW flooring is designed for outdoor areas that are expected to get wet.
The trickiest distinction is probably the difference between IW and IW+. The former is designed for floors that will get wet regularly, though they’re unlikely to get wet constantly (e.g., kitchen floors, grocery store floors). The latter is designed for floors that are designed to get wet constantly during use (e.g., shower floors, locker room floors).
O/G is a specialty category designed for car shops, commercial kitchens, and any other flooring that needs to withstand exposure to oil or grease.