Backlink

A backlink is a link on someone else's website that points to yours. The distinction from any other link is ownership: you did not place it. Someone else did, and that is the whole of its value.

Search engines began counting links in the late nineties because reading a page could not settle which of ten similar pages deserved to go first. Who points at whom is harder to fake than what a page claims about itself. That reasoning has survived every change since.

Not all backlinks weigh the same. A link from a site with real readers in a related field counts for a great deal; a link from a site that exists only to hold links counts for nothing at all. The gap is not one of degree — it is closer to a difference in kind, and buying the second sort mostly buys silence rather than penalty.

For AI answer engines the calculation widens slightly. A mention without a link still contributes: if credible sites in your field discuss what you do, a model reading the web has encountered your name in a context that makes sense of it. A site nobody has ever written about offers a model only its own account of itself, with nothing to weigh it against.