Definition
Extractability is how readily a machine can lift a correct, self-contained statement out of a page. It depends on the page being served as real HTML, on headings that match the questions being answered, and on paragraphs that stand alone.
Why it matters
Most AI crawlers do not execute JavaScript. A page whose content only appears after client-side rendering is, to them, an empty shell, and the site will never learn this from its own analytics.
How to measure it
Fetch the page without JavaScript and check that the answer text is present in the raw HTML. Compare the word count of the raw response against the rendered page; a large gap is the problem itself.