A high pressure line between the pumps and some point below a blowout preventer. This line allows fluid to be pumped into the well or annulus with the blowout preventer closed. (RP 53).
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}