The concept of an “influencer” is pretty clear. An Individual who can reach many people through various communication channels and can therefore, potentially, influence them to like or dislike, to adopt or ban, to buy or skip buying, products and services.
The more people the “influencer” can reach (read: the more “followers” they have), the better, stronger and more of an “influence” he or she has.
There is a whole marketing strategy called “influencer marketing” or “influencer outreach”. There is even a concept called “micro influencer” to describe people with less following who are still considered “important” in their niche.