A substance that changes the rate of a chemical reaction is called a catalyst. Catalysts speed up reactions without being consumed in the process, and they can be either organic or inorganic. They lower the activation energy required for reactions, making it easier for reactants to form products. Catalysts are crucial in various industrial processes, biological systems (like enzyme activity), and environmental reactions. Understanding catalysts allows for the optimization of chemical reactions, contributing to advancements in chemistry, biotechnology, and pharmacology.