This term "Annus mirabilis" was originally used to refer to which year?

Annus mirabilis (pl. anni mirabiles) is a Latin phrase that means "wonderful year", "miraculous year" or "amazing year". This term was originally used to refer to the year 1666, and today is used to refer to several years during which events of major importance are remembered. Prior to this, however, Thomas Dekker used the phrase mirabilis annus in his 1603 pamphlet The Wonderful Year, "Wherein is shewed the picture of London lying sick of the plague."

According to the Oxford English Dictionary, the first known written usage of the Latin phrase "Annus Mirabilis" is as the title of a poem composed by English poet John Dryden about the events of 1666. The phrase "annus mirabilis" translates as "wonderful year" or "year of miracles". In fact, the year was beset by great calamity for England (including the Great Fire of London), but Dryden chose to interpret the absence of greater disaster as miraculous intervention by God, as "666" was then regarded as the Number of the Beast, and the year 1666 expected by some to be particularly disastrous.

In addition to this, the English fleet defeated a Dutch fleet in the St James' Day Battle, for a great victory at sea. (However, in 1667 the Dutch burned several major warships of the English fleet in the raid on the Medway and Charles II was forced to sue for peace.)