the narrow, convoluted section of the intestines, extending from the pyloric end of the stomach to the large intestine and including the duodenum, jejunum, and ileum
See small intestine in American Heritage Dictionary 4
noun
The narrow, winding, upper part of the intestine where digestion is completed and nutrients are absorbed by the blood. It extends from the pylorus to the cecum and consists of the duodenum, the jejunum, and the ileum.