system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:When is referring to an expert opinion not considered an appeal to authority logical fallacy?
gpt
> The argument from authority (Latin: argumentum ad verecundiam) also appeal to authority, is a common argument form which can be fallacious, such as when an authority is cited on a topic outside their area of expertise or when the authority cited is not a true expert.

From Wikipedia, just for the rough definition.

So, something is an appeal to authority, when you are using someone's authority in another field to make claims in this one. Or you are pretending someone is an expert.

For example, Pele is an excellent soccer player. Using Pele's statements in an argument about the best way to play forward in soccer is not an appeal to authority because that is something he is genuinely knowledgeable in. He knows more than the average person. 

Using Pele's statements in an argument about blackholes is an appeal to authority because you are using his fame in another field to make arguments about a field he is not knowledgeable in. Pele doesn't know anything more than your average person about blackholes, so he should not be cited. Stephen Hawking, on the other hand, does know more than your average person, so he can be cited.