A nova is a nuclear explosion on the surface of a white dwarf star caused by accumulation of matter from nearby stars (mostly hydrogen). A single white dwarf can have several novae throughout its life.

During a supernova, enough material collects to make the star itself go kaboom. A supernova explosion can outshine an entire galaxy for a short time and build higher-mass elements, and birth new stars.

The matter falling on the white dwarf is usually from a close orbiting companion star still on the main sequence, which is why the nova can reoccur. It is the mass of a star which will determine whether or not it will go super nova.