When another site creates a link to your site, it is called a backlink.
Also known as inbound links, backlinks are a type of off-site SEO and are important because they represent a vote of confidence in your authority as a trusted source.
When multiple sites create backlinks to yours, Google recognizes the trend, infers that you must be credible, then rewards you with better positioning and visibility on the SERP.
Not all backlinks carry equal weight, however. A backlink from a recognized thought leader will drive SEO more than a backlink from a lesser-known site. The same is true for links that are followed when compared with those that aren’t.