Anorexia nervosa is defined as a refusal to maintain a healthy body weight due to an intense fear of gaining weight, and can lead to severe health complications if untreated. Pro-ana websites promote anorexia as a lifestyle choice and often create a community where users exchange tips and view anorexia as a form of empowerment. The document highlights the critical need for awareness and treatment of eating disorders, which can have devastating effects on individuals' physical and mental health.