Argument from authority

Argument from authority or appeal to authority is a form of argument or reasoning that argues if a person with authority in a field makes a statement about it, it is probably true. It could become a fallacy if it is misused.
In informal reasoning, the appeal to authority is an argument of the form:
The argument is good in some conditions. For example, a person says, "I need to take my medication because my doctor told me to." Doctors are trained, know much about medication, and probably have experience giving medication before. The person is appealing to a real authority with supported data that makes the authority probably right.
The argument is bad when there is a false authority or unclear authority. For example, "I know X is true because it said so on the internet." The complete internet has no authority because any person on the internet can say anything they want. A part of the internet may have authority, but it is unclear because the argument was not specific.