How clusters are built
Most often, queries are grouped by search results: if two phrases have a specified number of matching URLs in the top 10, it means the search engine responds to them with similar pages, so the phrases are placed in one cluster. You choose the match threshold yourself: the higher it is, the smaller and more precise the clusters. In addition to using clustering tools, the results are checked manually: similar search results do not always mean the same user intent.
What this means in practice
One cluster – one target page. If queries from one cluster are distributed across several pages, they will start competing in search results. Clusters also determine internal linking: pages within one cluster link to each other and to the main page for the topic.
Who it is critical for
For websites with more than a dozen pages targeting search: blogs, catalogs, and service websites with sub-services. A landing page for a single service usually has one cluster.