Alien Physiology, sometimes called "Extraterrestrial Biology", isn't so much a power as it is a reflection of the character's genetic heritage as a species not native to Earth ("heritage" as in a character's biological make-up, no matter how similar they may be in appearance to humankind). Individuals with an alien physiology are extraterrestrial, thereby excluding Atlanteans, Amazons, or others with unique or altered human physiology.
Although some of the abilities held by such races may be natural to their entire species, they are still alien to humans and are therefore termed "superhuman" or "super" abilities.
Prime examples of this category lie with the Legion of Super-Heroes. Although many members may appear completely identical to humans, their bodies can activate powerful and varied abilities, or function in ways that are unequivocally inhuman.