When something culminates, it reaches its highest point or final stage after a period of building up.

Think about a school year that culminates in a final project where you demonstrate everything you've learned. Or a mystery novel that culminates in a dramatic chapter where the detective reveals who committed the crime. A thunderstorm might build slowly with dark clouds and distant rumbles, then culminate in a downpour with lightning and thunder. A sports season culminates in championship games. Years of piano practice might culminate in a recital where you perform a difficult piece.

The word suggests a natural progression toward something significant. Things don't just end when they culminate: they reach a peak moment that feels like the purpose or destination of everything that came before. When you say a celebration culminated in fireworks, you mean the fireworks were the grand finale, the moment everything had been building toward. That sense of reaching a peak after a journey makes culminate more specific and powerful than simply saying something “ended” or “finished.”