The moment of highest intensity.
The point of no return.
The turning point.
The climax of any narrative is the most exciting moment, what everything has led to… when we see if the protagonist will win or lose. It’s the most pivotal moment in a narrative, and often is the measure of a narrative. A good climax leads to resolution and offers satisfaction to the reader. A weak climax does neither of those things.
It’s probably satisfying because it’s when the protagonist faces his or her fears, when the conflict is dealt with; often with internal conflicts, it’s when the protagonist has to grow and own his or her problems and learn from them.
In Cinderella, it’s when she loses her slipper as she escapes at midnight. She’s milked the most she can out of the ball; she’s enjoyed her evening of freedom; she’s fallen in love with the prince.
In “Marigolds” it’s when Lizabeth destroys Miss Lottie’s flowers AND realizes what she’s done. She realizes that she can’t fix it.
The climax is so important that it’s usually near the end o the story. The falling action is usually short, just a few events leading up to the resolution. In this instance, the falling action is her looking up at Miss Lottie, realizing her error, apologizing, and then the author flashes forward years and years to herself as an adult (back to before her flashback at the beginning of the story).