What is difference between catalyst and …

A reagent is a substance or compound added to a system to cause a chemical reaction, or added to test if a reaction occurs. The terms <i>reactant</i> and <i>reagent</i> are often used interchangeably—however, a reactant is more specifically a substance consumed in the course of a chemical reaction. <i><a href="https://en.wikipedia.org/wiki/Solvent" title="Solvent">Solvents</a></i>, though involved in the reaction, are usually not called reactants. Similarly, <i><a href="https://en.wikipedia.org/wiki/Catalysis" title="Catalysis">catalysts</a></i> are not consumed by the reaction, so they are not reactants. In <a href="https://en.wikipedia.org/wiki/Biochemistry" title="Biochemistry">biochemistry</a>, especially in connection with <a href="https://en.wikipedia.org/wiki/Enzyme" title="Enzyme">enzyme</a>-catalyzed reactions, the reactants are commonly called <a href="https://en.wikipedia.org/wiki/Substrate_(biochemistry)" title="Substrate (biochemistry)">substrates</a>.