The kolem was a Romulan energy unit.

In 2368, when the USS Enterprise-D was assisting a Romulan science vessel in restoring its main power systems, the Romulan officer Mirok was monitoring the power flow during the attempt to bring it back online. He reported that the power flow was "consistent at four hundred kolems" and there were "no fluctuations in frequency". (TNG: "The Next Phase")