Blowout Preventer 4 : A device attached to the wellhead that allows the well to be sealed with or without a string of pipe or wireline in the wellbore. (RP 54)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}