Crohn's disease is a type of inflammatory bowel disease that can affect any part of the gastrointestinal tract and is characterized by chronic inflammation. It presents with symptoms like abdominal pain, diarrhea, and fever. Microscopically, it shows features like ulcers, crypt abscesses, granulomas, and fibrosis of the intestinal wall. Complications can include anemia, malnutrition, strictures, fistulas, and in rare cases amyloidosis or bowel cancer.