(1) (vb.) Drilling. To take apart, disassemble and otherwise prepare to move the rig or blowout preventers. See: Blowout Preventer, Rig. (2) (n.) Well Completions. The process of disassembling well-control or pressure-control equipment on the wellhead. Depending on the configuration of the wellhead and casing strings, it may be necessary to nipple-down and nipple-up the blowout preventer (BOP) system as each casing string is run. Ant: nipple up, nipple-up. See: Blowout Preventer, Casing String