Any of the tubes that drain bile from the liver and gallbladder toward the intestine, a term often used interchangeably with bile duct. The network begins with microscopic canaliculi between liver cells, merging into ever-larger ducts until the common bile duct delivers bile to the duodenum. These ducts do more than passive piping: their lining cells modify bile by adding bicarbonate-rich fluid that protects the gut from acid. Disease of the ducts ranges from gallstone blockage to primary sclerosing cholangitis, an autoimmune scarring that strangles bile flow. Surgeons and radiologists map this anatomy meticulously, since operations and stents in the region demand exact knowledge of every branch. The biliary tree’s delicate plumbing reminds us that digestion depends on infrastructure as well as chemistry.