Peak means the highest point of something. When you climb a mountain, the peak is the very top where you can't go any higher. Mount Everest's peak rises 29,032 feet into the sky, higher than any other mountain on Earth.

The word also describes the moment when something reaches its greatest level. An athlete might be at their peak when they're in the best shape of their life, performing better than they ever have before. A singer's career might reach its peak when they're most popular and successful. When a movie theater is at peak hours, it's the busiest time with the most people buying tickets.

You can use peak as a verb too. A fever might peak at 103 degrees before it starts coming down, or interest in a new toy might peak right after it's released and then gradually fade.

As an adjective, peak describes something at its highest or best level, like peak speed, peak strength, or peak season for tourists. The phrase peak performance describes doing something at your absolute best. In each case, peak marks that crucial moment at the very top, whether you're talking about a mountain, a graph, or someone's abilities.