A kilt is a sort of human garment resembling a skirt. Many human cultures embraced this garment, including the Scottish, Irish, Romans, and Greeks.
In 2267, James T. Kirk, Spock, and Grang of the Wolf clan were forced to wear kilts as part of the Code Duello of Bavarya. (TOS novel: Mission to Horatius)
In 2276, a kilt was a common clothing item for Romulan servants. (TOS novel: The Romulan Way)