VSOP

To be graded VSOP Reserve, and marked with five stars, Cognac or Armanac brandy must have been stored in a cask for at least four years.

Confusingly, 'VS', which is used to designate brandy that's been stored for at least two years (and can also be marked with three stars), is usually expanded to 'Very Special'. I have seen VSOP given as Very Special Old Pale, but I think in this case 'Superior' is more correct.

According to Wikipedia, the use of the grading system is unregulated outside of Cognac and Armanac.