A rather chauvinistic term for any biological organism, whether Terragen or xenobiont, natural or tweaked, that requires extreme (non-Earthlike) environments for growth or metabolism; e.g. high temperature, acidity, pressure, radiation, toxic compounds, vacuum or near-vacuum, etc. There are extremophile sophont clades in the Terragen Sphere which inhabit cold temperature worlds, high temperature worlds, hi-radiation worlds, vacuum environments, and other environments which would would be fatal to nearbaseline humans.
Types of Extremophiles: Acidophile: An organism with a pH optimum for growth at, or below, pH 3.
Alkaliphile: An organism with optimal growth at pH values above 10.
Barophile: An organism that lives optimally at high hydrostatic pressure.
Halophile: An organism requiring high concentrations of salt for growth or optimal metabolism.
Hyperthermophile: An organism having a growth temperature optimum of 80°C or higher.
Psychrophile: An organism that requires or prefers cold for growth and metabolism. Common on some Europan planets and moons; in rare instances even evolve an intelligent star-faring civilization (the Muuh being the only known current example).