  We exhibit equivalent conditions for subspaces of an inner product space to
be isoclinic, including a characterization based on the classical notion of
canonical angles. We identify a connection with quantum error correction,
showing that every quantum error correcting code is associated with a family of
isoclinic subspaces, and we prove a converse for pairs of such subspaces. We
also show how the canonical angles for isoclinic subspaces arise in the
structure of the higher rank numerical ranges of the corresponding orthogonal
projections.
