What is "covering number"

n. (context graph theory English) The number of vertices in a minimum vertex cover of a graph, often denoted as $tau\; =\; tau(G)$.

In mathematics, a covering number is the number of spherical balls of a given size needed to completely cover a given space, with possible overlaps. Two related concepts are the packing number, the number of disjoint balls that fit in a space, and the metric entropy, the number of points that fit in a space when constrained to lie at some fixed minimum distance apart.