the most successful point of something
zenith - peak
The ‘zenith’ is an astrological term denoting the highest point reached by the Sun or Moon in the sky. Its meaning has been adapted to refer to the highest point of success in the development of something, or the peak of somebody’s achievements or talent.
I don’t want this period of success to be our company’s zenith. I want us to continue to develop and grow for years to come.
The author’s career reached its zenith in the 1950s. She never reached such heights again.
We had a great team, but one cup final was the zenith of our achievements.