Anorexia is a medical term for a loss of appetite. While the term outside of the scientific literature is often used interchangeably with anorexia nervosa, many possible causes exist for a loss of appetite, some of which may be harmless, while others indicate a serious clinical condition or pose a significant risk.

Anorexia is a symptom, not a diagnosis. Anorexia is not to be confused with the mental health disorder anorexia nervosa. Because the term 'anorexia' is often used as a short-form of anorexia nervosa, to avoid confusion a provider must clarify to a patient whether they are simply referring to a decreased appetite or the mental health disorder. Anyone can manifest anorexia as a loss of appetite, regardless of their sex, age, or weight.

The symptom also occurs in other animals, such as cats, dogs, cattle, goats, and sheep. In these species, anorexia may be referred to as inappetence. As in humans, loss of appetite can be due to a range of diseases and conditions, as well as environmental and psychological factors.