It stand for Very Special Old Pale or Very Superior Old Pale. Old pale because the quality of a pale cognac was so much better than that of a clear cognac. When cognac is first distilled is has no colour. After a few years of aging in wooden barrels it gets a pale colour. In the seventeenth century people had discovered that this pale cognac was very superior to the younger cognacs.
On the left the colorless eau-de-vie that comes right out of the pot still. On the right a young cognac that has aged two to three years in a barrel.