what is meant by catalyst?

Catalysis is the process by which the rate of a chemical reaction (or biological process) is increased by means of the addition of a species known as a catalyst to the reaction. What makes a catalyst different from a chemical reagent is that whilst it participates in the reaction, it is not consumed in the reaction. That is, the catalyst may undergo several chemical transformations during the reaction, but at the conclusion of the reaction, the catalyst is regenerated unchanged. As a catalyst is regenerated in a reaction, often only a very small amount is needed to increase the rate of the reaction