The few dozen inhabitants of a Gamma Quadrant planet that passes back and forth between ordinary space and a dimension in which they exist as pure consciousness.
The Meridians appear in the Deep Space Nine episode Meridian. Their planet spends sixty years at a time in another dimension, where its people have no bodies and do not age, and then returns to normal space for a short interval during which they are solid again. Each stay in our universe has been growing shorter, and only about thirty of them are left.
In 2371 the Defiant witnesses the planet appear and its crew is welcomed by the leader Seltin. Jadzia Dax and a Meridian named Deral fall in love while the officers study the star whose instability causes the shifts.
Dax works out how to lengthen future visits and decides to stay with Deral. Her body cannot make the transition, however, and her presence nearly destroys the planet. She is pulled back to the Defiant and must wait sixty years to see him again.