Shimano 12 mm Thru x 142 mm Shimano/SRAM 11 Speed Road Bicycle Rear Hubs
About Shimano - "Shimano practices good local citizenship, pursues continued access to those areas that are enjoyed by outdoor enthusiasts, and is committed to minimizing our impact on the environment."
This is hub spacing and is the width of the hub. It must match your frame specifications.
The cassette body type is the type of cassette and number of speeds the hub will accept.