the Glorious Twelfth

Từ điển Oxford Advanced Learner 8th

the Glorious Twelfth [the Glorious Twelfth] BrE NAmE
1. 1 12 August, the first day of the season for shooting ↑grouse (= a fat bird which is shot for sport and food) in Britain. Grouse shooting, especially on the Scottish moors, is very popular with rich people in Britain.
2. 2 12 July, the anniversary of the ↑Battle of the Boyne, which is celebrated by many Protestants in Northern Ireland.
See also ↑Orangeman