A lei was a traditional flowered garland from the Polynesian cultures of Earth. The garland was seen as a representation of the flowering of love and was worn around the neck.
During a party aboard USS Discovery on stardate 2136.8, Ash Tyler and several other crew members wore leis made of white imitation flowers. (DIS: "Magic to Make the Sanest Man Go Mad")
In 2373, Neelix created a Polynesian-type resort hologram program in which the crew of USS Voyager wore leis during a luau. (VOY: "Alter Ego")