The kilt was a traditional Human garment, typically worn by Human males of Scottish descent. It consisted of a length of tartan fabric (the tartan pattern often corresponding to the wearer's clan, home area or regimental allegiance) with sharp pleats in the back and flat aprons on the front; the kilt was worn with various dress accoutrements including a sporran (purse) in the front, shoulder plaid attached with a brooch, hose, and a wide kilt belt.
Montgomery Scott had two kilts: one red and black kilt was displayed on the wall of his cabin with its sporran, and he wore a white and gray kilt and accoutrements as part of his Starfleet dress uniform. (TOS: "By Any Other Name", "Is There in Truth No Beauty?", "The Savage Curtain").