A geodesic fold was a temporary gateway through space capable of bridging vast distances. Such a fold could be created by targeting the magnetic field of a red giant star with a verteron beam, causing a corresponding fold to open in the magnetic field of another red giant, providing a passageway between the two points. Although capable of providing a means by which great distances could be traversed, the high levels of geodesic radiation produced by such a fold would liquefy all organic matter, making the use of the phenomenon impractical for space travel.
In 2377, the crew of a Ferengi Marauder attempted to use a geodesic fold to acquire valuable Borg nanoprobes from Seven of Nine, a crewmember on the USS Voyager, by sending Voyager falsified information indicating that the crew could survive the trip. To do so, they intercepted a hologram of Reginald Barclay, which Barclay originally intended to assist the Voyager crew, and reprogrammed it to manipulate the crew into generating a fold with which to return to the Alpha Quadrant. The Ferengi would then obtain the nanoprobes, which they intended to sell for six bars of latinum per unit.
Taking position at a red giant in the Alpha Quadrant, the Ferengi initiated a geodesic pulse and opened the fold, causing a corresponding fold to open at a red giant in the Delta Quadrant. As the Voyager crew prepared to take the ship in, Lieutenant Barclay, posing as the hologram, contacted the Ferengi and convinced them that Captain Janeway had discovered a way to survive the geodesic radiation, but was intent on destroying their ship upon emerging from the fold. The Ferengi subsequently closed the fold, moments before Voyager could enter. (VOY: "Inside Man")