A subspace ghost is a type of subspace anomaly that manifested itself in nebulae and dust clouds. (RIS Bouteina: "There's no Coffee in the Nebula")

For some reason, subspace ghosts seemed to appear and disappear at random; when they did, though, they could make impulse drives go either much faster than normal or not work at all. Also, it made appear some nonsensical substances on the sensors, like coffee. (RIS Bouteina: "There's no Coffee in the Nebula")