A moment-angle complex $\mathcal{Z}_K$ is a compact topological space
associated with a finite simplicial complex $K$. It is realized as a subspace
of a polydisk $(D^2)^m$, where $m$ is the number of vertices in $K$ and $D^2$
is the unit disk of the complex numbers $\C$, and the natural action of a torus
$(S^1)^m$ on $(D^2)^m$ leaves $\mathcal{Z}_K$ invariant. The Buchstaber
invariant $s(K)$ of $K$ is the maximum integer for which there is a subtorus of
rank $s(K)$ acting on $\mathcal{Z}_K$ freely.