Anaerobic means "without oxygen." The term has many uses in medicine.
Anaerobic bacteria are able to survive and grow in environments that have no oxygen. This leads them to cause specific types of illness such as tetanus or gangrene.
Anaerobic exercise, such as weight lifting, uses energy produced by the body's metabolism that does not require oxygen. It generates lactic acid and usually cannot be sustained for long.
Illnesses in which the patient is deficient in oxygen can force the body to use anaerobic metabolism, generating harmful chemicals. This can happen in all types of shock.
Anaerobic is the opposite of aerobic.