A supernova is a spectacular stellar explosion, which for a brief time can outshine its host galaxy. These stunning stellar endings seed the cosmos with elements that give rise to stars, solar systems, and even life, while providing one of the best ways to measure distances in the Universe. They serve as standard candles at large distances revealing evidence for the accelerated expansion of the Universe.  LSST will dwarf the observations of supernovae to date as it discovers over 10 million of these spectacular events during its ten-year survey.  For more information, see wikipedia or TeachAstronomy.