When your favourite film directors talk about the movies they like, there's a good chance you'll go see them.
When your lawyer advises you against signing a contract, you probably aren't going to sign it.
And when your doctor tells you to change your diet because your cholesterol is too high, you're more likely to choose a side salad over fries the next time you're out for dinner.
When these subject matters experts say something, you take their words seriously because you know they're knowledgeable and you trust their opinions.
They can persuade you to change your behaviour: to think and act differently than you would have otherwise.
These are your Influencers.
We don't usually think of doctors and lawyers when we hear the term "Influencers", though; we're more likely to think of athletes and actors with millions of Instagram followers, or social-media celebrities with hilarious TikTok videos.
Let's be clear: celebrities can absolutely be Influencers. I bought a bottle of Aviation Gin because I'm a big fan of actor Ryan Reynolds, and he suggested multiple times (and in very funny ways) that I should give it a try. I own a pair of Under Armour running shoes because I see Dwayne "The Rock" Johnson wear them when he's working out, and I thought having a pair would help me get in shape. (Note: simply owning a pair of Project Rock running shoes does absolutely nothing for your fitness. Apparently, you have to actually use them.)
But these two celebrities are Influencers for me because they caused me to purchase the products they were endorsing instead of the products I would otherwise have bought. You might admire these two talented individuals as much as I do, but if they haven't persuaded you to think or act differently in some way, they're not -- by definition -- an Influencer for you.