A special case of a Flag Manifold. A Grassmann manifold is a certain collection of vector Subspaces of a Vector Space. In particular, is the Grassmann manifold of -dimensional subspaces of the Vector Space . It has a natural Manifold structure as an orbit-space of the Stiefel Manifold of orthonormal -frames in . One of the main things about Grassmann manifolds is that they are classifying spaces for Vector Bundles.