A decade is a 10-year period, often used to refer to a period of time in history or for measuring the passage of time. DECADES are commonly referred to by their starting year, such as the 1980s or the 1990s. DECADES are also used to measure the progress of a particular field or industry, such as the digital decade or the space age. DECADES can also be used to refer to a period of time in which a particular event or trend occurred, such as the roaring twenties or the golden age of Hollywood.