A secondary antibody specifically binds to a primary antibody but ideally not to any antigen that is present in the specimen to be analyzed. Usually secondary antibodies are conjugated to an enzyme, a fluorophore or other labels that allow detection of the primary-secondary antibody complex.
Species specific secondary antibodies have a strong preference for primary antibodies originating from one species. This allows multiplex stainings in which several primary antibodies from different host species are combined in one experiment.
