The rank of grand admiral or grand-admiral was a grade of admiral in a naval service organization that was equivalent to or outranking of a fleet admiral. The flag officer rank of grand admiral was used by service organizations, including in the 23rd century by senior staff at the highest levels of the Federation Starfleet.
In 2285, Stephen Turner was the grand admiral serving as one of Starfleet's head officers. His service uniform appeared to be essentially standard for a Starfleet flag officer, but his formal uniform as Starfleet grand admiral was markedly different from the uniforms worn by other Starfleet officers. The maroon officer's tunic had two shoulder tabs ornamented with rank insignia and both wrist cuffs had a unique braid on them. Optional uniform accessories included an undershirt with ornamented collar, a white sash, and award ribbons that were worn above the brass Starfleet insignia.
By the 24th century, Pavel Chekov had reached the rank of grand admiral, and was considered the foremost authority of Starfleet. In 2375, Jean-Luc Picard felt very strongly in his opposition to Starfleet orders to allow the Ferengi to donate sensor technology to the planet Halkan—so much so, in fact, as to feel that he would disobey even Chekov's orders, if they had indeed been the orders that put him at odds with Captain Christine MacDonaldin that situation.