Re: COOL Aliens!
When a creature from a planet other than Earth looks like a human, sounds like a human, acts somewhat like a human and gets confused for a human.
Their internal physiology may well be different, whether a little or a lot, but otherwise they appear to be the genuine article.
In-story, this occasionally leads to a Handwaving story about how all the races have some common ancestor. Other times, it gets justified by using a Transplanted Humans story. Out-of-story, this is often explained by the fact that there are remarkably few non-humanoids in the SAG or Equity. Other explanations include the idea that a humanoid form is the natural result of any evolutionary path (Humans Are Special on Evolutionary Levels). Recent research may hint at this being true to some extent; many species seem to be engineered by evolution for maximum fuel efficiency. The bipedal human body has remarkable agility and stamina for its size, though there are some notable flaws like weak joints and a narrow birth canal. Although our impressive cognitive abilities and incredibly complex social structure evolved to counter these. There's also a real phenomenon known as "Convergent Evolution" whereby species that originated in different areas eventually develop into things that look similar because it's a useful form.
This trope also covers shape-shifters who budget-savingly stay in human form around humans.
The bottom rung of the Alien ladder, below Rubber Forehead Aliens and Intelligent Gerbils. Note that, for this trope, the alien must be visually indistinguishable from a human. "Human, but with blue (or purple, orange, green, etc.) skin" falls under Rubber Forehead Aliens. Aliens with cultural rather than biological similarities fall under Inexplicable Cultural Ties.