External link
An external link is a link that points from one website to a different website, as opposed to an internal link between pages of the same site.
An external link is a link from a page on one website to a page on a different website. If Fernhill Coffee's brewing guide links to a study on a university's site, that's an external link. A link from the guide to Fernhill's own shop page is an internal link.
The same link has two names depending on where you stand. To Fernhill, the link to the university is an outbound link. To the university, it's a backlink. SEO tools and people use "external link" for both, so it helps to check which one they mean.
Why they matter
Links between sites are how search engines discover pages and how they judge which ones others trust. Links into your site from other sites help your pages get found and rank. Links out from your site help your readers check your facts and find more.
A page full of claims with no sources asks readers to take your word for it. Linking to where your facts come from makes the page more useful and more believable. Google's link best practices ask for links with descriptive words that make sense out of context.
Mark the links you don't vouch for. Paid links get rel="sponsored", links in comments get rel="ugc", and anything else you don't want to stand behind gets rel="nofollow", as Google explains in its guide to qualifying outbound links.
External links and AI answers
AI answers are full of external links of their own: the sources they cite. When an answer links to a review, a directory or your own site, that link is how readers check the answer, and it's often how an AI visitor arrives at your site.
The external links on your pages help too. A page that cites good sources for its facts is easier for anyone, people or platforms, to trust and check.
For example, Harrow & Pine's page on sustainable oak links to the certification body's listing of its suppliers. When an assistant answers "is Harrow & Pine's wood sustainably sourced?" it can read the claim and the proof together.
In AnswerOrbit
Sources shows every page the answers used for your prompts and how many times each one was linked. Citation share is your website's share of all the links in the answers. See Sources and What the numbers mean.