Decade ("60s" or "sixties"), although this may leave it uncertain which century is meant. These references are frequently used to encapsulate popular culture or other widespread phenomena that dominated such a decade, as in "The Great Depression of the 1930s" or "The Roaring Twenties". However, the Gregorian calendar begins with the year 1. (There is no year "zero", and the year before AD 1 is 1 BC with nothing in between.) Therefore, its "first" decade is from AD 1 to AD 10, the "second" decade from AD 11 to AD 20, and so on. So, although "the 1960s" comprises the years
Decade 1960 to 1969, "the 197th decade" spans 1961 through 1970. A decade may also refer to an arbitrary span of ten years. For example, the statement "during his last decade, Mozart explored chromatic harmony to a degree rare at the time", merely refers to the last ten years of Mozart's life without regard to which calendar years are encompassed. Particularly for the 20th century, a nominal decade is often used to refer not just to a set of ten years but rather to a period roughly approximating those ten years - for example, the phrase "the sixties" often refers to