In stellar evolution, an FU Orionis star (also FU Orionis object, or FUor) is a pre–main-sequence star which displays an extreme change in magnitude and spectral type. One example is the star V1057 Cyg, which became 6 magnitudes brighter and went from spectral type dKe to F-type supergiant. These stars are named after their type-star, FU Orionis.