Heyday

n.joyful, hopefuleveryday

What it means

The period when a person, activity, or institution had its greatest success, strength, or popularity.

Reach for it when locating a recognized peak while avoiding the assumption that all later work declined

In its heyday, the theater presented a new community production every month.

playful
glory days
nostalgic affection for past success is intentional
not when Glory days often implies present decline and can sound self-congratulatory.
everyday
high point
one especially successful phase should be named plainly
not when A single high point can interrupt an otherwise weak period; a heyday is sustained.
everyday
prime
a person's or thing's strongest period is meant
not when Prime can refer to physical condition or readiness, not public success.
professional
peak
the highest measured level is the relevant fact
not when Peak can last only a moment and carries less historical character than heyday.
formal
zenith
the absolute high point suits elevated prose
not when Zenith is grand and singular, while a heyday can extend across years.
literary
golden age
a whole era is remembered for flourishing achievement
not when Golden age can romanticize the past and omit who was excluded from its benefits.

in its heyday
In its heyday, the mill employed craftspeople from six villages.
during the heyday
During the heyday of rail travel, the station served overnight routes.
return to its heyday
The club does not need to return to its heyday to serve today's neighborhood well.

The definition and the example on this page are written here. The dictionaries above ground which meaning is being described, not the wording.