1. A polypeptide hormone that is secreted by the beta cells of the islets of Langerhans in the pancreas and functions in the regulation of carbohydrate and fat metabolism, especially the conversion of glucose to glycogen, which lowers the blood glucose level. It consists of two linked polypeptide chains called A and B.

2. Any of various pharmaceutical preparations containing this hormone or a close chemical analog, derived from the pancreas of certain animals or produced through genetic engineering and used in the medical treatment and management of type 1 and type 2 diabetes.