Anastomosis: The connection of normally separate parts or spaces so they intercommunicate. An anastomosis may be naturally occurring or artificially constructed and be created during the process of embryonic development or by surgery, trauma or pathological means.

An anastomosis may, for example, connect two blood vessels (as in a naturally occurring arteriovenous anastomosis, a connection between an artery and a vein) or it may connect the healthy sections of the colon or rectum after a cancerous or otherwise diseased portion has been surgically removed. A gastrojejunal anastomosis connects the stomach directly with the jejunum.

The term "anastomosis" comes straight from the Greek. It originally referred to an opening or junction through a mouth as of one body of water with another. Anastomosis has been in medical usage since the Greek physician Galen (129-200 AD) used it to describe the interconnections between blood vessels. The plural is anastomoses.