noun

• (biology, anatomy, embryology) The caudal part of the alimentary canal of an embryo, including the colon and the rectum, in humans and some other animals.
• (biology, anatomy, medicine) The developed counterpart in the adult: the most distal part of the alimentary canal, which in humans is generally defined as comprising the distal third of the transverse colon, the splenic flexure, descending colon, sigmoid colon, and anorectal junction.