A deuterium pump is a mechanism utilized onboard starships for the purpose of facilitating the physical movement of deuterium towards the ship's deuterium injectors for injection into the warp core.
In 2152, after being disabled by a mysterious vessel, the Enterprise NX-01's chief engineer, Commander Charles Tucker III, began efforts to re-initialize the ship's warp engines, a process which included priming the deuterium pumps. (ENT: "The Crossing"