Share of sources
Share of sources is the part of all the pages AI answers used that came from one website, such as yours or a competitor's.
Share of sources is the part of all the sources in a set of AI answers that come from one website. Count every page the answers used, then work out what share of them came from your site, or from a competitor's, or from a review site.
It tells you how much of the material the platforms build their answers from is yours. The more of it that comes from your pages, the more say you have in what the answers say.
How it's counted
Take the answers to your prompts over a period. List every source they used. Then count how many of those sources are on each website, and divide by the total.
For example, 140 answers about coffee subscriptions use 600 sources between them. 60 are pages on Fernhill Coffee's site, 90 are on Kestrel Roasters' site, and 120 are on one big review site. Fernhill's share of sources is 10%, Kestrel's is 15%, and the review site's is 20%.
That tells Fernhill two things. Kestrel's own pages are read more than Fernhill's. And one review site supplies a fifth of everything the platforms read on the subject, which makes it worth a close look.
Sources and citations
People often use share of sources and citation share as if they meant the same thing. They can differ. A source is any page an answer used. A citation is a page the answer actually links to. Some answers read a page without linking to it.
So pick one, say which you're using, and stick to it. A chart that mixes the two is comparing different things.
In AnswerOrbit
The Domains tab in Sources lists every website the answers used, with how many answers used it and how many times it was linked. Under citations, Citation share is your website's share of all the links in the answers. What the numbers mean has the definitions.