Vector equilibrium is a Buckminster Fuller term to indicate the most perfectly balanced energetic geometry. In 3D the form is traditionally known as the cuboctahedron, and is classified as one of the 13 Archimedean Solids. What makes this form the vector equilibrium is that its centre point is the same distance from its vertexes as its connected vertexes are from each other. Another thing that makes it special is that when spheres cluster together they naturally make this form. My friend Marshall Lefferts has some great information about it here