decade

A decade is a period of ten consecutive years. The word originates from Old French decade, from Latin decas and Greek dekas, all meaning ten.

In calendar usage, a decade is typically defined as the ten-year interval beginning with a year that ends in 0 and ending with a year that ends in 9. For example, 1980–1989 is the decade commonly called the 1980s. In common speech, the label of a decade usually refers to that calendar span; in historical writing, a decade can also denote a culturally defined period whose features may not align perfectly with calendar boundaries.

Decades are useful for analyzing social, economic, and demographic trends, allowing researchers to observe longer-term changes while smoothing over year-to-year fluctuations. They sit between the year and the century in scale, providing a convenient unit for historical and statistical discussion. Notable historical decades include the 1920s, often associated with cultural change in many Western countries, and the 1960s, linked with significant political and social movements. The concept also appears in data presentation, where ten-year aggregations can simplify comparisons across time and geography.