Pack year means

(B) 20 cigarettes per day for 1 year# A pack-year is a quantification of cigarette smoking.> 1 pack-year is equal to smoking 20 cigarettes (1 pack) per day for 1 year, or 40 cigarettes per day for half a year, and so on.> Number of pack-years = (packs smoked per day) * (years as a smoker).