What does it mean?
Stellar (star) formation – the process by which stars are formed.
Molecular cloud – Also sometimes referred to as a stellar nursery if new stars are being formed within the cloud. Molecular clouds are giant regions of diffuse gases that can be as big as 326 light years (3.1 x 1015 km) across. They are composed mostly of Hydrogen and Helium, with a few other elements dispersed throughout. Internal gravitation in denser regions of the cloud can trigger the collapse of parts of the cloud, and when this happens, new stars can be formed.
Supernova – The explosion of a star near the end of its lifetime, as it runs out of nuclear fuel in its core. Only massive stars can become supernovae. Supernova explosions are so bright they can be easily observed in other galaxies.