(covers information from several alternate timelines)
A fireworks display was a celebratory event comprised of explosions of light and sound given off by a firework or other light source.
In 2371, Benjamin Sisko and his son Jake successfully navigated a replica of an eight hundred-year-old Bajoran spaceship from Deep Space 9 to Cardassia, giving evidence to the theory that ancient Bajorans had done the same. Upon reaching Cardassia, they were greeted with fireworks. (DS9: "Explorers")
In early 2373, Enrique Muniz, who was in delirium shortly before his death, mistook the Dominion's ultritium concussion shell bombardment of the ship he and others were trapped in on Torga IV, as a fireworks display like those of the Carnival he had attended as a youth in Spain. (DS9: "The Ship")