Backlink

A backlink is a link from another domain pointing at yours. Search engines have treated links as endorsements since PageRank in 1998: a page that trusted pages link to gets treated as more trustworthy itself. Not every link carries the same weight. The nofollow, sponsored, and ugc rel values declare the relationship, and Google treats them as hints rather than a promise to throw the endorsement away. They cover most comment threads, press releases, and paid placements, and how much value survives is the engine's call, not yours.

What actually earns them: original data, a free tool people bookmark, a strong opinion others cite when they argue, and being the obvious reference for one narrow subject. Relevance beats volume. One link from a respected site in your topic outweighs fifty from unrelated directories.

Gotcha: link schemes are the fastest route to a manual penalty. Bought links, private blog networks, and link exchanges run at scale for the links alone are exactly what spam systems are tuned to catch. Two sites in the same field happening to cite each other is not a scheme, it is how the web has always worked; the excessive, systematic version is the problem. And a hard-won backlink pointing at a URL you later delete lands on a 404 and buys you nothing. Long redirect chains are not free either: every hop costs crawl budget and latency for bots and humans alike. Keep your URLs stable.