Eternals were a mythological race sung of by poets of Kelis' species. They believed that these beings could live on their planet and walk among them as beings of great power, such the power to make the ground open up and the sky to fall, and other strange events. There were different clans.
In 2376, Kelis, a poet on his homeworld believed B'Elanna Torres to be an Eternal, after seeing the advanced technology she used aboard the crashed Delta Flyer, including the use of a dermal regenerator to heal herself, and the coincidental outbreak of a storm when she angered. While recalling the events that stranded the USS Voyager in the Delta Quadrant, Torres suggested to Kelis that the Caretaker himself was also an Eternal, and that their enemies were the Borg. (VOY: "Muse")