How does clustering work?

Keyword Insights uses live, country-specific SERP data for each query. We check every keyword in the top 10 results and, if a keyword shares 40% or more URLs in common, we’ll determine that they are a cluster. There is also a little NLP weaved in and some other clever logic, but essentially this is how it functions. The name of the cluster is based on the keyword within that cluster with the most search volume.