A content cluster is a group of related pages that together cover a topic in depth, anchored by a pillar page and made up of focused supporting pages on individual subtopics. The pages interlink, so the pillar points down to each supporting page and each supporting page points back up.
For brands, content clusters are how you build genuine coverage of a subject rather than a scattering of unconnected posts. The structure concentrates authority on the pillar, helps search and AI systems see that you cover the topic comprehensively, and ensures that whatever specific question a user asks, there is a focused, citable page to answer it.