Indexability

Indexability is whether a fetched page is allowed into the index. It's the step after crawlability: a bot can read your page, but signals like a noindex tag, a canonical pointing elsewhere, or thin or duplicate content can keep it out of the index — and only indexed pages are eligible to be retrieved and cited.

It belongs to the access pillar because crawlable-but-not-indexed is a silent, common failure. The usual culprits are an accidental noindex directive, canonical tags consolidating a page away, or content so thin the engine declines to store it. Auditing for these — and making sure each page you want cited is genuinely indexable — closes the gap between "a bot can read it" and "an engine can actually use it."

Example. A page with a stray <meta name="robots" content="noindex"> left over from staging is perfectly crawlable but will never be indexed — so it can never be cited, however good it is. Removing the tag restores its eligibility.