A backlink is a link from one website to another. It is an important factor in SEO (Search Engine Optimization) because search engines like Google consider backlinks as a sign of trust and credibility. When a website has many high-quality backlinks, it is more likely to rank higher in search results. Backlinks can be do-follow (which pass SEO value) or no-follow (which do not pass SEO value but still drive traffic). Building strong backlinks from reputable sites can improve a website’s visibility and authority.