A link from another website to your website.
A backlink is an incoming link from another website. From the other publisher’s perspective, it is an outbound link; from your perspective, it is a backlink. It can point to the homepage or a specific resource, product or service page. The exact destination matters because it determines what the reader finds after following the reference.
Backlinks can help people discover a business and provide context about what a page offers. Google also uses link-analysis systems within its ranking processes. That does not make every link equally valuable or turn the number of links into a complete measure of credibility. The referring page, its relevance and the reason for the link all deserve inspection.
A sensible business objective is a useful reference that makes sense to the other publisher’s audience. That is different from arranging links primarily to manipulate rankings. Paying for an advertisement can be legitimate, but commercial links need appropriate qualification. A claimed authority score or promised quantity does not by itself establish that a placement is appropriate.
Takeaway: Evaluate the actual page and audience behind a backlink. Favor genuinely useful references over packages sold mainly on link counts or assurances of ranking gains.
Example
A woodworking association publishes a guide to identifying timber and references a member workshop’s original species comparison chart. The backlink leads directly to that chart, giving readers the information mentioned in the guide rather than depositing them on an unrelated sales page.
What to check
Check that the link still reaches the intended resource and that your page remains useful. When reviewing a proposed placement, ask why the publisher’s readers would benefit from it and whether any payment or sponsorship needs to be disclosed and qualified.
For more detail, see Google ranking systems guide.