An SEO backlink is a link from an external website that directs users to your website. Backlinks are important for SEO because they help search engines determine the credibility and authority of your site. When other reputable websites link to your content, it signals to search engines that your site is trustworthy and valuable, which can improve your rankings in search results. The more high-quality backlinks a website has, the higher its chances of ranking well on search engines.