A dramatic climax in a story is the point of the highest action just before the plot is resolved. It generally takes place very late in the story, with the subsequent denouement lasting only short time before the story's end.
A story contains rising and falling tension throughout, during which the potagonists find themselves in worse and worse trouble. Each peak in tension is called a crisis. The dramatic climax of the story is the final and worst crisis. This is the breaking point of the tension, when the hero and villain come face-to-face for an ultimate showdown, or the hero has to make a final sacrifice. A few stories have more than one climax, but this is uncommon.