Extended definition
Link from another site to your site. Backlinks are the main authority signal Google uses. Quality matters far more than quantity.
Context and application
Backlinks remain a top 3 ranking factor in 2026, according to all major studies. But the definition of “backlink quality” has refined: thematic relevance (link from SEO site to SEO site > link from auto site to SEO site), DR/DA of source site, real traffic of source page, dofollow vs nofollow. The most powerful backlinks come from: digital PR (mentions on news sites), guest posts on authoritative sectoral sites, partnerships with complementary tools. The weakest: comment spam, generic directories, link farms — can attract penalty.
In practice
1 backlink from a relevant sectoral site > 100 backlinks from generic directories.