Anorexia nervosa is a type of mental disorder that belongs in the category of eating disorders. According to the National Institute of Mental Health’s website, “an eating disorder is an illness that causes serious disturbances to your everyday diet, such as eating extremely small amounts of food or severely overeating.”
There are a lot of other characteristics associated with eating disorders as well, such as an unhealthy obsession over body size and weight, and feelings of being out of control when it comes to food and dieting. Specific criteria used to diagnose people with anorexia can be found in the Diagnostic and Statistical Manual of Mental Disorders (DSM).
Anorexia nervosa specifically is defined by an abnormal and unhealthy sense of body image and self-esteem, extreme diet restrictions, a fear of adding on any pounds. The person with anorexia nervosa diets to reach an unhealthy body size.
https://www.empowher.com/mental-health/content/keep-celebrating-world-mental-health-day-learn-about-anorexia-nervosa