Younger stars still in the hydrogen-burning stages are defined by their position in the main sequence graph of star development, but once the hydrogen core burns away, stars take differing paths of development, depending on mass. Low and high mass stars undergo generally similar stages of development, first expanding into giants and then collapsing into their remnant cores. Low mass stars end life as white dwarfs, but higher mass stars end life in supernova explosions, leaving behind neutron stars or, for stars with very high mass, black holes.
Star mass can be defined in terms of solar mass. Low mass stars, having a mass less than three times that of Earth's sun, pass through a gas-giant phase and eventually become white dwarf stars. High mass stars, however, fall into two categories: those having a mass greater than three times solar mass, and very massive stars, at 10 times or greater the mass of the sun.
Once the hydrogen core burns away, a star begins to burn heavier elements, expanding into a giant star. In high mass stars, eventually all elements are burned away until only iron remains and no more fusion is possible. At that point, a final expansion of neutrinos sends the star into a massive explosion, resulting in a supernova. The degenerate core of a high mass star that remains after a supernova explosion is called a neutron star.
Very massive stars, those having more than 10 times the mass of the sun, undergo the same stages of evolution as other stars as they burn heavier and heavier elements. However, given their mass, when fusion ceases to take place the core collapses much farther. The resulting supernova explosion leaves the ultra-dense remnant known as a black hole.