A colonoscopy is a medical procedure where a flexible tube called a colonoscope is inserted through the rectum to examine the large intestine (colon) and sometimes the lower part of the small intestine. The colonoscope has a camera and light at its tip, allowing the doctor to visualize the colon's lining and detect abnormalities like polyps, inflammation, or cancer. Colonoscopy is commonly used for screening, diagnosis, and treatment of various colorectal conditions. It is a valuable tool in preventive healthcare, particularly for detecting colorectal cancer early when treatment is most effective.