ASA - 1:  Normal healthy patient (e.g. non-smoker, minimal alcohol intake)

ASA - 2:  Mild systemic disease without substantial functional limitations (e.g. smoker, social drinker, pregnancy, obesity with BMI 30-40, well-controlled diabetes or increased blood pressure, mild lung disease)

ASA - 3:  Systemic illness with substantial functional limitations (one or more disease, e.g. poorly controlled diabetes or blood pressure, COPD, morbid obesity with BMI > 40, alcohol abuse, cardiac pacemaker, reduced cardiac function, end-stage kidney failure with dialysis, premature infant, heart attack, stroke or cardiac stents within last 3 months)

ASA - 4:  Severy systemic disease that is a constant threat to life (recent heart attack, stroke or cardiac stents, severe heart valve dysfunction, severe reduction in heart function, sepsis, deranged clotting, acute kidney dysfunction)

ASA - 5: Moribund patient who is not exepcted to survive without the operation (e.g. ruptured aortic aneurysm, massive trauma, major bleed into the brain, ischaemic bowel due to underlying cardiac disease, multiple organ / system dysfunction)

ASA - 6:  A declared brain-dead patient whose organs are being removed for donor purposes

This classification has been developed by the American Society of Anaesthesiologists (ASA), and it is being used in the planning of patient care before, during and after the operation.

It can also be used to estimate the risk of a patient to suffer a complication after an operation (Morbidity, e.g. infection, kidney failure, compromised blood pressure) or the risk of dying within the first 30 days after an operation (Mortality)

Reference: 

American Society of Anaesthesiologists (last reviewed in Oct. 2014: https://www.asahq.org/resources/clinical-information/asa-physical-status-classification-system)