What term refers to a period of one thousand years, often associated with a time of great joy?

The correct term that refers to a period of one thousand years is "Millennium." This term is commonly used in various contexts, especially in historical discussions or cultural references, often to denote significant periods of time marked by notable events or advancements. The association of the millennium with a time of great joy may stem from various celebrations and cultural milestones that occur at the turn of each millennium, which are often viewed as moments of reflection and anticipation for future progress.

In contrast, a century refers to a period of one hundred years, an epoch is a substantial segment of time characterized by particular events or developments, and a decade indicates a span of ten years. Each of these terms defines a different time frame, highlighting the uniqueness of a millennium as a thousand-year interval.