A disease is a condition that impairs normal functioning of the body or mind. It can be caused by various factors, including genetic disorders, infections, environmental factors, lifestyle choices, or a combination of these. Diseases can range from minor to severe and can affect one or multiple systems within the body. Some common diseases include heart disease, diabetes, cancer, and infectious diseases such as the flu or COVID-19. The presence of a disease often results in symptoms that can impact an individual's health and quality of life. Treatment for diseases may include medication, therapy, lifestyle changes, or surgery.