Weston's is a large nursery in Hopkinton, MA originated by the Mezzit family. The PJM rhododenron was first hybridized there. The initials stand for Peter J Mezzit. The real, registered name name for your plant is 'Weston's Pink Diamond'. Some sellers tack on the PJM label to indicate it is a PJM type: small leaved and hardy. This renaming only creates confusion and is not a good or approved practice.