A Cluster ID is a CipherTrace ID for a collection of addresses associated with an Input Cluster. The Cluster ID is a way of grouping The term "Bitcoin" can either refer to Bitcoin the network, ... More addresses into one group that is likely to be controlled by a single user or by a service. Note that one entity may control more than one cluster. Therefore, users should not equate the “Cluster ID” with all addresses likely to be controlled by an attributed or unattributed private key holder.
There are a number of ways to compute an Input Cluster. One way is the “Multi-input is a way of associating multiple addresses with ... More clustering” method, where we analyze multi-input transactions and associate them with known patterns. Also note that these groupings may not be 100% accurate.