(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 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")