A<unk>  is a clinical quantification of cigarette smoking used to measure a person's exposure to tobacco. This is used to assess their risk of developing lung cancer or other pathologies related to tobacco use. However, it is difficult to rely on the assessment based on the<unk>  due to the different nature of the<unk> aging by different companies.
Pack-year
Dose 
Background radiation equivalent time
Never event
Deemed status
Regimen
Roll-your-own cigarette
Lifetime reserve days