This from google: The highest conditioned cull cows are reported as "Breakers". They usually are quite fleshy and generally have excellent dressing percentages. Body condition score 7 and above are required to be "Breakers". The next class is a more moderate conditioned group of cows called "Boners" or "Boning Utility". The four classes are divided primarily on fatness. The fattest cows are called "Breakers." Moderately fleshed cows are "Boners." Thin cows are called "Leans" or "Lights," depending upon the weight of the cow.