Here's what that means:

* Luminosity classes describe a star's absolute magnitude (its intrinsic brightness).

* Class V indicates that the star is fusing hydrogen into helium in its core, like our Sun. This is the most common type of star, and it's what we call a main sequence star.

So, the Sun is a main sequence star, fusing hydrogen in its core, and that's why it has a luminosity class of V.