A backlink is a hyperlink on one website that directs users to a page on another website. Often referred to as "inbound" or "incoming" links, backlinks are a key factor in search engine optimization (SEO) because they signal to search engines that the linked-to content is valuable and trustworthy. High-quality backlinks from reputable sites can improve a website s authority and ranking in search results, while low-quality or spammy backlinks can have the opposite effect.