You're at your high school reunion. Someone asks about a classmate who didn't come to the reunion. You've heard that she's a movie producer, so you say this.
She's a big shot in Hollywood now.
A "big shot" is an important person.
This phrase sometimes has a little bit of a negative tone. You can call someone a "big shot" if they have a high-paying job but don't have time to pay attention to their old friends, for example. Or if you want to tease a friend who's bragging too much, you can say:
All right, Mr. Big Shot!
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