This document defines and provides examples of different types of extremophiles - organisms that thrive in extreme environments. It discusses thermophiles, which grow best at high temperatures, mesophiles that prefer moderate temperatures, halophiles that require high salt concentrations, and psychrophiles capable of growth in cold temperatures. Each type is classified and key examples are provided, such as thermophiles including Thermus aquaticus and hyperthermophiles above 80°C. The document also outlines how these extremophiles are able to survive through unique enzymes and membrane adaptations.