Backlink is a link from another website that points to your website.
It matters because organic search compounds over time when pages are technically accessible, useful, differentiated, and connected to real search intent. Clear SEO terminology also helps teams avoid shortcuts that create long-term risk.
Example
A chamber of commerce directory links to a member’s website. That is a backlink to the member site; its existence alone does not establish the relevance, endorsement or ranking effect of every link from that directory.