Vorilium

From Memory Alpha, the free Star Trek reference.

Vorilium (or vorillium) is a substance with propulsion system applications. Main engineering aboard the USS Voyager was usually short on vorilium during its time in the Delta Quadrant.

In 2373, the Mikhal Traveler Zahir informed Captain Kathryn Janeway that the star system in his fellow Traveler Nakahn's fanciful story about a "moon creature" also contained asteroids rich in vorilium. Janeway remarked that the substance might be worth a short detour. (VOY: "Darkling")

Later on stardate 50698, a Voyager away team led by Chakotay found vorilium on a planet. During this mission, Harry Kim was separated from the group for a time and became infected with a Taresian retrovirus. (VOY: "Favorite Son")