cluster analysis
task of grouping a set of objects in such a way that objects in the same group (called a cluster) are more similar (in some sense or another) to each other than to those in other groups (clusters)
en-GB/ˈklʌstə əˈnæləsɪs/
en-US/ˈklʌstɚ æˈnælɪsɪs/