Osteoarthritis is a common chronic, progressive, degenerative joint disease that affects cartilage and bone within a joint. It most often affects older adults but can also occur in younger people. It is a leading cause of physical disability. Osteoarthritis can be classified as primary, with no known cause, or secondary, due to an underlying condition like injury or obesity. It involves the breakdown and eventual loss of cartilage in one or more joints. Symptoms include pain, stiffness, and reduced mobility. Diagnosis is based on symptoms and confirmed with x-rays showing signs of cartilage loss. Treatment focuses on reducing pain and improving joint function through lifestyle changes, physical therapy, braces, and in some cases surgery.