A robe was a type of clothing.
Septos wore the tan robes of a Romulan merchant as part of his cover. Dellas wore a gray robe when she traveled to 2293 to kill Spock. (TOS novel: Assignment: Eternity)
In 2377, Benjamin Sisko donned a dark, hooded robe when he wanted to visit Deep Space 9 incognito. (DS9 novel: Warpath)