Pillar page
A pillar page is the reference content for a cluster: it covers an entire subject, targets the broadest relevant query, and distributes links to satellite pages that develop each aspect in detail.
In practice
Long-form — often 2,000 words or more — but structured for fast reading: a table of contents, self-contained sections, compact answers at the top of each heading. Pillar pages age well when updated; their revision date and data freshness both contribute to their credibility.