Each boss kill gets a parse from 1 to 100: how its healing per second compares with recent Classic Era kills of that boss (the last 12 weeks) at the same raid size, by players of the same spec, or of the same role while a spec has too few kills to compare with - always as the role they really played that night (100 = the best). A boss parse is the middle (median) of their kills of that boss, so one unlucky or lucky night barely moves it; a raid parse the average of the bosses in that raid, and the Personal Parse the average of their raids. Best is the average of their best kill of each boss: what they do on a good night. See how it's calculated →