What is Backlink?
A backlink is a link from one website to another. When site A links to site B, site B has a backlink from site A. Backlinks are one of Google's top 3 ranking factors.
Backlinks act as votes of confidence. The more high-quality, relevant websites that link to your content, the more authority search engines assign to your pages. Not all backlinks are equal — links from authoritative, topically relevant sites carry more weight than links from low-quality or unrelated sites.
Key metrics: referring domains (unique sites linking to you), domain authority of linking sites, anchor text relevance, and link placement (editorial links in content are more valuable than footer links).
Example
If Search Engine Journal publishes an article and links to your blog post about technical SEO, that's a high-quality backlink from an authoritative, relevant source.