Heyday (noun)

1. The period of time when someone or something is at their peak or most successful.
2. A time of great prosperity, success, or happiness.

Origin:

The word "heyday" comes from the old english word "hēa dæg" which means "high day" or "holiday".

Examples:

1. The company's heyday was in the 1990s when they dominated the market.
2. He remembered the heyday of his youth with fondness.
3. During the heyday of the Roman Empire, it was the dominant power in the world.
4. The singer's heyday was in the 1980s when she released several hit songs.
5. The city's heyday as a cultural center was in the early 20th century.