A decade is a period of 10
Although any period of ten years is a decade, a convenient and frequently referenced interval is based on the tens digit of a calendar year, as in using "1960s" to represent the decade from 1960 to 1969. Often, for brevity, only the tens part is mentioned (60s or sixties), although this may leave it uncertain which century is meant. These references are frequently used to encapsulate
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 events that took place between c. 1964 and 1972, and to memories of the