(usually plural) a device with an explosive that burns at a low rate and with colored flames; can be used to illuminate areas or send signals etc.
source: WordNet 3.0
A device for producing a striking display of light, or a figure or figures in plain or colored fire, by the combustion of materials that burn in some peculiar manner, as gunpowder, sulphur, metallic filings, and various salts. The most common feature of fireworks is a paper or pasteboard tube filled with the combustible material. A number of these tubes or cases are often combined so as to make, when kindled, a great variety of figures in fire, often variously colored. The skyrocket is a common form of firework. The name is also given to various combustible preparations used in war.