An intelligence officer was a title given to an officer aboard a starship or space station who was responsible for intelligence matters. The officer typically kept in contact with a central organization, such as Starfleet Intelligence, for the latest information.
Aboard Deep Space 9, Lieutenant Commander Worf held the position upon accepting assignment there. Doctor Julian Bashir briefly assumed the post in late 2373 while Worf was serving on the IKS Rotarran. Only Bashir or Jadzia Dax could fill in for Worf, as only Starfleet officers with a class four security clearance could hold the position. He told Chief Miles O'Brien "All I can do is read these fascinating reports and analyses, and analyses of analyses and then keep it all to myself. Because no one else has a 'need to know'". (DS9: "The Way of the Warrior", "Soldiers of the Empire")