Not to be confused with
Nova.
A supernova is the explosion of a giant star. It usually happens when the nuclear fusion in the star cannot hold the core against its own gravity. The core collapses, and then explodes.
The biggest stars that make supernovae are hypergiants and smaller ones are supergiants. They are massive: because of gravity, they use up their energy very quickly. Normally they only live for a few million years.