  Based on the entropy concept, we define a new clustering order parameter $c$
feasible for finite systems of interacting oscillators. Unlike the generalized
synchronization order parameters of the Kuramoto type, this new order parameter
singles out the splay state as the unique state with $c = 0$, thus yielding a
positive value whenever there is some kind of cluster formation in the system.
It is therefore proposed to be monitored alongside the Kuramoto order
parameters as a means to quantify the overall amount of clustering in the
system.
