  Equi-chordal and equi-isoclinic tight fusion frames (ECTFFs and EITFFs) are
both types of optimal packings of subspaces in Euclidean spaces. In the special
case where these subspaces are one-dimensional, ECTFFs and EITFFs both
correspond to types of optimal packings of lines known as equiangular tight
frames. In this brief note, we review some of the fundamental ideas and results
concerning ECTFFs and EITFFs.
