A Diamond Jubilee is a celebration held to mark a 75th anniversary, such as the length of time someone's very elderly grandparents have been married. But in the case of the British monarchy, the celebration marks the 60th year that a monarch has reigned.
Queen Elizabeth II, who acceded the throne of the United Kingdom and other Commonwealth countries upon the death of her father, King George VI, on February 6, 1952, celebrates her Diamond Jubilee this year (2012). The official date of her 60th anniversary as monarch was Feb. 6, but events are being held across her realm throughout the year.
The main Diamond Jubilee celebration is planned for June 2 – 5. On Sunday (June 3), a flotilla of more than 1,000 ships will sail down the River Thames, with the Queen aboard the Royal Barge. The following day, a network of 2,012 beacons will be lit throughout the Commonwealth (the group of nations, mostly former members of the British Empire, which recognize the queen as their ceremonial ruler).
Other weekend events include a nationally-televised concert, luncheon, church service and, of course, plenty of royal waving from the balcony of Buckingham Palace. [Why is the Color Purple Associated with Royalty?]
But why does a monarch's Diamond Jubilee come after 60 years, when everyone else must wait 75? Special circumstances: No British monarch has ever reigned for 75 years, and so, before 1897, none had ever celebrated a Diamond Jubilee. That year, Queen Victoria reached her 60th year as monarch. She had largely withdrawn from public life after the death of her beloved husband Albert in 1861. To celebrate her reign and reconnect her with the public, it was decided to bring the Diamond Jubilee forward to her 60th anniversary, and the change in official procedure stuck.