A catalyst in a chemical reaction is a substance that increases the reaction rate without being consumed in the process. Catalysts work by lowering the activation energy required for the reaction to occur, providing an alternative pathway that allows reactants to transform into products more easily. This principle is crucial in various chemical processes, including industrial synthesis, biochemical reactions in living organisms, and environmental applications such as catalytic converters in vehicles. Understanding how catalysts function is essential for developing efficient chemical processes and technologies.