Eclat 12 mm Thru x 142 mm Shimano/SRAM 8/9/10; Shimano Dynasys 11 Bicycle Rear Hubs
About Eclat - "Simplicity is the hardest design principle to follow; It's at the heart of our approach to eclat."
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.