The Glorious Twelfth is usually used to refer to 12 August, the start of the shooting season for Red Grouse (Lagopus lagopus scoticus) and to a lesser extent the Ptarmigan (Lagopus muta) in the United Kingdom.
This is one of the busiest days in the shooting season, with large amounts of game being shot. The date itself is traditional, the current legislation enshrining it is the Game Act 1831 (and in Northern Ireland, the Wildlife (Northern Ireland) Order 1985). Not all game (as defined by the Game Act 1831) have the same start to their open seasons - most begin on September 1, with October 1 for Woodcock and Pheasant.
Since UK law says that the start of the season cannot begin on a Sunday, it is sometimes postponed to 13 August, as in 2001 and 2007. Because grouse are not and never have been reared to any extent for shooting, their numbers fluctuate naturally from year to year. In recent years, the Glorious Twelfth has also been hit by hunt saboteurs, the 2001 foot and mouth crisis (which further postponed the date in affected areas) and the effect of sheep tick, heather beetle, the gut parasite Trichostrongylus tenuis and severe flooding and bad weather. In some seasons where certain moors are hit by low numbers of grouse, shooting may not occur at all or be over by September.
One can be sure that members of the Royal Family will be out today shooting in the Balmoral Estate.