(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 2370, Gideon Seyetik described the process of reigniting the dead star Epsilon 119 and stated, that at the end the crew of the USS Prometheus could "just stand back and watch the fireworks." (DS9: "Second Sight")
In 2371, Keiko O'Brien asked Miles O'Brien if fireworks were part of the traditional celebration of "I'm Married to the Most Wonderful Woman in the Galaxy Day"; he assured her they were In a manner of speaking). (DS9: "The House of Quark")
Later that year, Benjamin Sisko and his son Jake successfully navigated a replica of an eight hundred-year-old Bajoran lightship from Deep Space 9 to the Cardassian system, giving evidence to the theory that ancient Bajorans had done the same. Upon reaching the system, they were greeted with fireworks by three Galor class vessels. (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")