A microorganism able to grow well between 20°C and 45°C, having an optima of 30°C to 40°C. Many can sustain growth at below 10°C albeit very slow growth.

Microorganisms which thrive at medium temperatures (20-370C or 68-990F).

A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, typically between 25 and 40 °C (77 and 104 °F). The term is mainly applied to microorganisms.