Aquiel Uhnari wearing a wig
A wig or toupée was an artificial piece of hair, most often worn for fashion or traditional reasons.
At one time, it was fashionable for Betazoid women to wear elaborate wigs that caged small animals. The practice, which was cruel to the animals, was stopped when one (unknown) woman stood up against it. (TNG: "Half a Life")
Lwaxana Troi used to wear wigs from time to time. (DS9: "The Forsaken")
Aquiel Uhnari's sister Shianna always thought her sister would look good with a wig. Uhnari tried it out in 2369 but was not too impressed, as was Geordi La Forge. (TNG: "Aquiel")
While trying to come up with character sketches for possible stories, Jake Sisko once watched a Bolian from an the upper level of Deep Space 9's Promenade, and speculated that he was wearing a toupée in order to impress a Dabo girl. (DS9: "The Muse")
Dala wore a wig while impersonating Kathryn Janeway. (VOY: "Live Fast and Prosper")