A QumpIn was a Klingon title and position for those that worked within the Klingon Empire. It was the equivalent of a starship's first officer.

In the Mirror Universe, Regent Worf while on the IKS Negh'Var demanded from his QumpIn to be put in communications with the port authority at Khitomer. After the assassination of his best friend Duras, Worf left the QumpIn to command the Negh'var while he determined his friends death. (DS9 novel: Dark Passions)

It's unknown whether there is a counterpart title within the Klingon Empire in the standard universe.