Tubing 4 : Pipe installed in the wellbore inside all casing strings and extending from the wellhead to an elevation at or above the formation, and through which formation fluids normally are transported to the surface. (RP 54)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}