Decade

A decade is a period of time consisting of ten consecutive years. It is also known as a decennium. The word 'gu'' (season) in Somali is one of the terms used to mark the year, since gu' refers to the main rainy season in the annual cycle.

A decade is an intermediate time span between a year and a century. One century contains ten decades. Historians, economists, and scientists use the decade to mark changes, because the period is long enough for change to become visible, yet short enough to allow detailed analysis.

Methods of counting

Two methods are common. The first divides decades by tens: the years 1990 to 1999 are called 'the nineties'. The second is based on arithmetic counting beginning from year 1, so a decade runs from 1991 to 2000. The first method is more widely used in general usage and the media.

Use in culture and history

People use decades as cultural and political markers. For example, terms such as 'the sixties' or 'the seventies' refer to particular music, fashion, or political conditions of that period. Such categorization is informal and imprecise, since social change does not follow numerical boundaries.

Other uses

In climate science, economics, and statistics, ten-year cycles are often used to identify the effects of particular years that deviate from normal patterns. Development plans by governments and international organizations also frequently base their projections on ten-year periods.