Given a point lattice, a cluster is a group of filled cells which are all connected to their neighbors vertically or horizontally.

Stauffer, D. and Aharony, A. Introduction to Percolation Theory, 2nd ed. London: Taylor & Francis, 1992.

CITE THIS AS:

Weisstein, Eric W. "Cluster." From MathWorld--A Wolfram Web Resource. http://mathworld.wolfram.com/Cluster.html