Peaked describes something that has reached its highest point and often suggests decline afterward. When a band's popularity has peaked, they were once at the top of the charts but aren't as popular anymore. If someone says your performance peaked in the second quarter, it means you played your best then but didn't maintain that level later.

A company's profits might have peaked in the 1990s, meaning they've never earned that much since. An athlete who peaked early might have been incredibly talented as a teenager but never improved beyond that.

You can also say someone peaked too soon if they used up all their energy or effort before the moment that really mattered. Imagine studying intensely for a test three weeks early, then forgetting everything by test day.

The word sometimes appears in the phrase past their peak, describing someone or something that was once excellent but has declined: “That restaurant was amazing five years ago, but it's past its peak now.”