"The peak" refers to the highest or most extreme point of something, like a mountain or performance. It marks the top level of strength, activity, demand, or quality before things decline.
A man's dignity isn't measured by the people he has around him when he's at the peak of his success, but by his ability not to forget those who helped him when his need was greatest. Paulo Coelho
However, it is safe to say that at the peak in 1929 the number of active speculators was less - and probably was much less - than a million. John Kenneth Galbraith
The peak of the [Presidential] campaign happened in Albuquerque, where a local reporter said to me, "Dr. Commoner, are you a serious candidate or are you just running on the issues?" Barry Commoner
Now the peak of summer's past, the sky is overcast And the love we swore would last for an age seems deceit. Cecil Day Lewis
And, so I set my goals on astronaut because, as a military aviator, it was, I considered that to be about the peak of a flying career. Duane G. Carey
It's better to finish at the peak or soon after it, than to wait until the audience notices a decline. Eberhard Weber