Backlinks are important to SEO. When another site links to your site, a backlink is created. If, for example, a brand finds one of your blog posts that’s helpful for their customers, they might link to it. That backlink, as Moz puts it, is “vote of confidence” in your content. 

Backlinks are important to SEO because search engines see all of those votes of confidence as evidence that your content is valuable. If lots of sites link back to yours, search engines are more likely to surface your content in search results, improving your ranking for the topics linked to. 

Earning backlinks is an essential part of off-site SEO, and obtaining more backlinks is called link building. But like so many aspects of SEO optimization, link building is not straightforward. Most backlinks are good, some are great, and others are toxic. Too many toxic backlinks can harm your ranking.