A decade is a period of ten years. When historians talk about “the 1960s” or “the 1990s,” they're referring to decades. Your grandparents might reminisce about what life was like a decade ago, meaning ten years back in time.

We often use decades to organize history and track change. The Roaring Twenties (the 1920s) brought jazz music and economic boom, while the 1980s saw the rise of personal computers and video games. Each decade tends to develop its own character through the events, inventions, and cultural shifts that happen during those ten years.

People sometimes mark personal milestones by decades too. Turning ten means you've lived one decade. Someone celebrating their 50th birthday has lived five decades. When you hear that a scientist spent decades researching a cure, it emphasizes the length and dedication of that work: multiple stretches of ten years, perhaps twenty or thirty years of continuous effort.