A utopia is a place of ideal perfection.
Jonathan Archer called Crewman Daniels native time of the 31st century a utopia. (ENT episode & novelization: Shockwave)
The Traveler described his homeworld as a utopia. (TOS comic: "Dark Traveler")
The Platonians called their society on Platonius a utopia. (TOS episode: "Plato's Stepchildren")