Alien Physiology, sometimes called "Extraterrestrial Biology", isn't so much a super 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.
It should be noted however, that although every alien being has physiology that is different than that of an Earthling, this doesn't always make them superior to Earthlings. For example, the character known as Snitch is an alien, but his race is of a small stature compared to humans, so he would be considered far weaker, on the other hand, this could also make him harder to catch, as he could hide in small places a human would not be able to access due to their larger size.
Another example is the Balunians. Although they possess abilities that humans do not, they are also far more fragile than humans, due to their balloon-like bodies, which make them especially vulnerable to sharp objects. A small prick on the finger could be enough to kill them, as all of the air in their bodies would be released.