Decade (dec) Conversions
A decade is a period of 10 years. The word is derived (via French and Latin) from the Ancient Greek: δεκάς, romanized: dekas, which means a group of ten. Decades may describe any ten-year period, such as those of a person's life, or refer to specific groupings of calendar years.
Any period of ten years is a "decade". For example, the statement that "during his last decade, Mozart explored chromatic harmony to a degree rare at the time" merely refers to the last ten years of Wolfgang Amadeus Mozart's life without regard to which calendar years are encompassed.