Before revision:  A polycube is an object constructed by gluing cubes face-to-face . An edge-unfolding cuts edges on the surface and unfolds it to a net, a non-overlapping polygon in the plane.
After revision:  A polycube is an object constructed by gluing cubes face-to-face ) has an edge unfolding, that is, cuts along edges of the cubes that unfolds the polycube to a single nonoverlapping polygon in the plane.