The Rukani sector was possibly a region of space in the Delta Quadrant controlled by the Rukani. It was mentioned in the holodeck program Insurrection Alpha. (VOY: "Worst Case Scenario")
As the Rukani were only mentioned in the Insurrection Alpha program and did not appear on-screen, it is possible that this region did not actually exist and was merely created for the program by Lieutenant Tuvok.