A Diamond Jubilee is a celebration held to mark a 75th anniversary, but only the 60th anniversary in the case of a monarch (i.e. length of time a monarch has reigned).
Traditionally, the diamond jubilee or anniversary of a person was also on the 75th anniversary. This changed with the diamond jubilee of the British Queen Victoria's reign. There was considerable national unrest when Queen Victoria largely withdrew from public life after her husband's death in 1861. It was decided to bring the diamond jubilee forward to the 60th anniversary on 22 June 1897. The Diamond Jubilee of Queen Elizabeth II, celebrated on 2 June 2012, was only the second in the country's history.
In South Asia, the term is also used for certain 100-week anniversaries. For instance, in both India and Pakistan, a diamond jubilee film is one shown in cinemas for 100 weeks or more.
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