(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 from the Prakesh and two other Galor-class Cardassian vessels. (DS9: "Explorers")
As a youth in Spain, Enrique Muniz witnessed fireworks displays at the Carnival he attended in his boyhood. In 2373, Muniz, who was in delirium shortly before his death, mistook an ultritium concussion shell bombardment, which the Dominion fired at a ship he and others were trapped in on Torga IV, as a fireworks display like those of the Spanish Carnival. (DS9: "The Ship")
In an alternate timeline, the Delta Flyer reached Earth by using a quantum slipstream drive in 2375. Upon arrival at the planet, the shuttlecraft and its occupants were received with an antimatter fireworks display. (VOY: "Timeless")