An influencer is an individual whose actions and opinions carry more weight with their colleagues, social network and the general public than is the case with most other individuals.
Influencers include journalists, subject experts, celebrities and other individuals with large followings. They typically have established online presences through multiple channels and large followings on social media platforms such as Facebook and Twitter and are widely considered authorities among their follower base. In IT contexts, influencers are often early adopters who are looked to for guidance.
In a social media marketing context, the more influence a person has, the more appeal that individual has to companies or other individuals who want to promote an idea or sell a product. Influencer marketing is an approach that seeks to maximize the effectiveness of efforts by targeting individuals who have the ability to affect the actions and opinions of a sizeable audience of prospective customers.