Ultra Light Cushion: A thin set "barrier" between your skin and footwear. Expect the thinnest structure here, used in liner socks and similar.
Lightweight Cushioning: Ultra Thin cushioning footbed for a lightweight thin barrier between footwear and sole but with some foot structure for optimum fit. Used in run socks.
Original Weight Cushion Level: Consider the Original Weight as a conventional everyday weight sock similar to what most of us would buy from your local Marks' for example. Some foot structure but no specific foot cushioning to speak or.
Mid Weight Cushion Level: Slightly heavier fabrication with a modest amount of under-foot cushioning perticularly at the heel and toes to protect against impact and protect the metatarsal. These offer good durability and comfort in conventional shoes but are less likely to be worn as a liner sock but rather as a sock in their own right.