Yield grade is based on backfat, Yield grade 1 being the leanest, 5 with the most fat covering.
Quality grade is based on marbling or intramuscular fat, Select, Low, medium, high, choice and prime.
Killer cows are normally listed as Canner, Cutter, and Breaking, I think around here. These won't be used for much but hamburger, or dog food on the other end of the spectrum.
