Topic cluster
A topic cluster organizes content around a pillar page: the pillar covers the theme broadly, satellite pages develop each sub-question in depth, and internal links make the hierarchy explicit. Together they signal subject-matter breadth to search engines.
In practice
The benefit is twofold: users find a complete path through the content; the engine understands the knowledge structure on offer. A cluster is planned around query fan-out — the actual range of sub-questions users ask — rather than a theoretical outline. Satellite pages left unlinked to the pillar lose most of their value.