사람이나 사물이 가장 번성하거나 기운이 왕성한 시기.
The period of a person's or thing's greatest success, popularity, or vigor.
예문:
"The band's heyday was in the 1980s when they topped the charts globally."
"In the heyday of the steam engine, railways transformed the landscape of the country."
"She was considered the most influential fashion designer during her Parisian heyday."