A supernova is a star that has exploded at the end of its life. Only special stars undergo supernovae; the sun will not experience a supernova when it dies. Supernovae occur in stars that have more than 10 times the mass of the sun.
Toward the end of their lives, massive stars run out of hydrogen to convert into helium. These stars then start forming more massive elements such as carbon and oxygen from the helium. In its final days, a massive star turns silicon into iron. This type of fusion reaction causes a star to collapse. The star then ejects its outer portions in a spectacle of light and energy called a supernova. A supernova produces light many times brighter than the star ever had.