I have seen countless times the adjective "compact" in astronomy, e.g. compact stars, compact binaries, etc. I would like to know, what exactly is this supposed to mean? From this source, I am led to believe that "compact" is meant to denote objects of the greatest matter densities in the universe, i.e. white dwarfs, neutron stars, and black holes. Is this correct?
Compact stars are stars of great density; stellar remnants in which the fermion constituents have become degenerate. i.e. white dwarfs and neutron stars (though sometimes black holes would be included).
A compact binary is a binary star system containing at least one compact object.