Microorganisms capable of growing under extreme physicochemical conditions such as high temperatures, pressures, and acidity.

A catch-all term for organisms living in harsh conditions. The definition of "extreme" environments is usually a taxonomic one, meaning an environment where only a restricted range of organisms can live.

A group of organisms whose growth is dependent on extreme environmental conditions, e.g., extreme halophiles, extreme psychrophiles, extreme thermophiles.

Term coined for (micro)organisms which live in (relatively) extreme conditions of temperature, pH, salt content, etc.

organisms (typically bacteria) that are adapted to living in extreme conditions, such as high salt, in ice or in thermal springs.

Creatures that live comfortably in environments formerly considered lethal, such as those that are very hot or lack oxygen.