Define Pasteurization and Sterilization - thermal processing?

Pasteurization: Pasteurization is a mild heat treatment to kill part of the microorganisms present in food. This process is usually combined with another preservation method. So primary objective of pasteurization is to kill pathogenic (milk) or spoilage (beers, fruit juices) microorganisms

Commercial Sterilization: Sterilization is the most extreme heat treatment given for the preservation of food. Usually target organism is a heat resistant microorganism, most often a spore or schlerotia forming organism rather than a vegetative one (e.g. spore forming anaerobic bacteria - Clostridium botulinum).