The honor guard was a special detachment of Starfleet crewmembers who provided a ceremonial welcome to visiting dignitaries.
In 2268, the honor guard from the USS Enterprise was summoned to the hangar deck by Pavel Chekov to greet Ambassador Sarek's party. (TOS: "Journey to Babel")
In 2376, an honor guard stood by while Lieutenant John Kelly's body was fired into space. (VOY: "One Small Step")