The "Appeal to Celebrity" logical fallacy is accepting a claim of a celebrity based on his or her celebrity status, not on the strength of the argument.
Most celebrities are actors and athletes and not experts in the products or causes they endorse. There are, of course, some exceptions. Some celebrities use their fame and fortune to promote causes they believe in and know a lot about. For example, Matt Damon knows a lot a about charter schools and vouchers - and produced a documentary on the topic because he is upset about the Republican agenda to undermine education.
Example: The Hill reported that Susan Sarandon, an actress, said that it wouldn't be much smoother with Hilary Clinton as president. How is this news? Susan Sarandon is an ACTRESS not a political scientist, journalist or political analyst. How can she predict what might or might not have happened. Who cares what Susan Sarandon thinks - except maybe her family and friends.