A photoinitiator is a chemical compound that initiates a polymerization process when exposed to light, typically ultraviolet (UV) or visible light. It absorbs the light energy and generates reactive species, such as free radicals or cations, which start the chemical reaction that leads to the hardening of materials like resins and coatings. Photoinitiators are widely used in various applications, including 3D printing, adhesives, and inks. They play a crucial role in industries such as cosmetics and electronics, where rapid curing and solidification of materials are essential for product performance and durability.