What it is
A backlink is just a link on someone else's site that points to a page on yours. One credible site linking to you is a small public vote that your page is worth a look. Search engines have counted those votes for two decades, and the AI systems now writing answers lean on the same idea of earned trust.
Why it matters
This is the trust layer of the search-engine and AI-system audiences. When an AI tool decides which of ten possible sources to quote, it favors pages the wider web already vouches for. Strong backlinks do not guarantee a citation, but weak ones make you easy to skip. If respected sites in your category never reference you, AI has little reason to treat you as the authority.
What to do
Earn links the durable way: original research, useful tools, and content other people in your field actually want to reference. Audit your existing backlinks for spammy or broken ones, and prioritize a handful of high-credibility mentions over a pile of low-quality links.