Command level officer or command officer was a high-ranking officer with certain given privileges.
Commander Rogerson of the US Navy's USS Enterprise was the command duty officer when the Russian spy Pavel Chekov was found aboard in 1986. He also referred to himself as Command Officer Rogerson. (Star Trek IV: The Voyage Home)
In Starfleet, the trial board for a mutiny required "no less than three command officers." For Spock's mutiny trial aboard the USS Enterprise, the three available command officers present where Captain James T. Kirk, fleet captain Christopher Pike, and Commodore José I. Mendez. (TOS: "The Menagerie, Part I") Years later, when Janice Lester was posing as James T. Kirk, she/he ordered a court martial of Spock, with lieutenant commander's Montgomery Scott and Leonard McCoy served on that trial board. (TOS: "Turnabout Intruder")
Several of the senior officers aboard the USS Enterprise-D, including William T. Riker, Data, Beverly Crusher, Deanna Troi, and Geordi La Forge were considered among the ship's command officers. During a period in 2364, when Captain Jean-Luc Picard was possessed by a Beta Renner entity, the senior officers discussed how to deal with the change in the captain's mentality. Doctor Crusher determined that she could enter a medical log citing her evidence, along with an agreement between the command officers, and with the support of the first officer. Riker, as the second-in-command, would have need to ultimately make the final decision. (TNG: "Lonely Among Us")
Rear Admiral Brand's investigation into the Nova Squadron's crash, and the resulting death of Joshua Albert, required two command level officers to complete. In that case, it was her along with Vulcan Captain Satelk. (TNG: "The First Duty")
For Nog, a non-Federation citizen, to attend Starfleet Academy he needed a letter of reference from a command level officer before they could take the entrance exam. In his case, he was able to receive this letter from Benjamin Sisko, captain of Deep Space 9. (DS9: "Heart of Stone")
In order for Kellin to make a temporary modification to USS Voyager's sensors, if she could gain access the ship's astrometrics processors, she could have made the modification permanent. Captain Kathryn Janeway approved of the work, but informed her that she would need a command officer with her to override the security lockouts. Chakotay volunteered to assist. (VOY: "Unforgettable")