The peak of a process or an activity is the point at which it is at its strongest, most successful, or most fully developed.

When something peaks, it reaches its highest value or its highest level.

The peak level or value of something is its highest level or value.

Peak times are the times when there is most demand for something or most use of something.

A peak is a mountain or the top of a mountain.

The peak of a cap is the part at the front that sticks out above your eyes.