There are two ways to measure a star's brightness:

* Apparent magnitude: This is how bright a star *appears* to us from Earth. It's influenced by both the star's actual luminosity and its distance from us.

* Absolute magnitude: This is how bright a star *would* appear if it were 10 parsecs (32.6 light-years) away from us. This gives us a more accurate measure of the star's actual luminosity, independent of its distance.

So, while "brightness" is a general term, "luminosity" is the more specific term used in astronomy to describe a star's intrinsic light output.