A backlink is just one website linking to another. Sounds boring. It is also one of the strongest trust signals in search, which is why people have spent two decades trying to game it.
The short version
A backlink is a hyperlink from one website to another. Search engines treat backlinks as signals of trust and authority, so links from credible, relevant sites can help a page rank higher.
Why backlinks carry weight
Each quality link is a kind of vote. When trusted sites point to you, engines infer your content is worth surfacing. The catch is that not all links are equal. One link from a respected, relevant source beats a hundred from spam.
Most pages have none
Backlinks are also rarer than people assume. Ahrefs research across hundreds of millions of pages found that the majority have no referring domains pointing to them at all. That gap is both the problem and the opportunity our SEO and ecommerce work goes after.
FAQ
How many backlinks do I need to rank?
There is no magic number. Relevance and authority of the linking sites matter far more than the count. A few strong links usually beat many weak ones.
Can backlinks hurt my site?
Spammy or manipulative links can. Earning links naturally from credible sources is the safe and durable approach.
Sources
Ahrefs, search traffic study: https://ahrefs.com/blog/search-traffic-study/