Diverticulitis is an inflammation or infection of diverticula, which are small pouches that can form in the walls of the colon. When these pouches become inflamed or infected, it can lead to symptoms such as abdominal pain, fever, and changes in bowel habits. Treatment typically involves antibiotics, dietary changes, and in severe cases, surgery may be required. It's often associated with a low-fiber diet and is more common in older adults.