The order of reaction refers to the power to which the concentration of a reactant is raised in the rate law equation of a chemical reaction. It indicates how the rate of the reaction depends on the concentration of each reactant and which reactant has the greatest effect on the reaction rate. The overall order of a reaction is the sum of the exponents of all reactant concentrations in the rate law. For example, in a rate law like rate=k[A]x[B]y\text{rate}=k[A]^x[B]^yrate=k[A]x[B]y, the reaction order with respect to A is xxx, with respect to B is yyy, and the overall order is x+yx+yx+y. Reaction orders can be zero, meaning the reaction rate does not depend on that reactant's concentration, or first, second, third order, etc., indicating proportional influences of the reactant concentrations on the reaction rate. The order of reaction is determined experimentally and is essential for understanding reaction kinetics and mechanisms.