What a backlink is
A backlink, sometimes called an inbound link, is a hyperlink on someone else's website that points to a page on yours. The site doing the linking is the referring domain. The page being linked is the target.
Every backlink carries a piece of metadata called anchor text, the visible words that form the link. Anchor text is one of the cues Google uses to understand what the linked page is about.
Why backlinks still matter
Google's original PageRank algorithm was built on the insight that links are editorial endorsements. A page that many other respected pages link to is more likely to be a useful answer. Two decades later, after countless updates, links remain among the top three ranking signals.
Not all links are equal. A link from the New York Times or a university research page carries far more weight than a link from a low-quality forum. Quality, relevance, and the trust of the referring domain all matter more than raw count.
Good links versus bad links
Good links are earned because the linking site genuinely thought your content was worth referencing. They come from sites that are topically relevant to yours, that have their own audience, and that have not been penalized by Google.
Bad links come from link farms, paid placements without disclosure, link exchanges at scale, and comment spam. Modern Google is good at detecting these patterns. The penalty for a bad link profile is usually a quiet loss of rankings rather than a manual action, but in egregious cases it is a manual penalty that requires a disavow file and a reconsideration request to recover from.
How to earn backlinks ethically
Publish content that genuinely deserves to be linked to: original research, in-depth guides, useful tools, opinionated takes on topics you understand. Then do the outbound work of telling people the content exists. Reach out to journalists covering your space. Pitch guest articles to sites your customers read. Get listed in legitimate industry directories. Sponsor events and nonprofits that publish a sponsor page.
Link building is the slowest and most expensive part of SEO, but it is also the most defensible. A site with a strong link profile holds rankings through algorithm updates that punish weaker competitors.