Anorexia nervosa is a psychiatric diagnosis that describes an eating disorder characterized by low body weight and body image distortion with an obsessive fear of gaining weight. Individuals with anorexia are known to commonly control body weight through the means of voluntary starvation, purging, vomiting, excessive exercise, or other weight control measures, such as diet pills or diuretic drugs. It primarily affects adolescent females, however approximately 10% of people with the diagnosis are male. Anorexia nervosa is a complex condition, involving neurobiological, psychological, and sociological components.Lask B, and Bryant-Waugh, R (eds) (2000) Anorexia Nervosa and Related Eating Disorders in Childhood and Adolescence. Hove: Psychology Press. ISBN 0-86377-804-6.

The term anorexia is of Greek origin: a (?, prefix of negation), n (?, link between two vowels) and orexis (??????, appetite) thus meaning a lack of desire to eat. Costin, Carolyn.~ (1999) The Eating Disorder Sourcebook. Linconwood: Lowell House. 6. A person who is diagnosed with anorexia nervosa is most commonly referred to with the adjectival form anorexic. The noun form, "anorectic" is generally not used in this context and usually refers to drugs that suppress appetite.

"Anorexia nervosa" is frequently shortened to "anorexia" in both the popular media and television reports. This is technically incorrect, as the term "anorexia" used separately refers to the medical symptom of reduced appetite (which therefore is distinguishable from anorexia nervosa in being non-psychiatric).