In this paper, we revisit the role of polarization and coherence in the study of polarization speckle. It is shown that the type of polarization and coherence used in such analysis has an important difference from the "classical"polarization and coherence concepts. The analogy between polarization speckle and partially polarized thermal radiation is explored. We propose a concept referred to as ensemble-average polarization and coherence for statistical optics and give the definition and physical indication for polarization speckle. Some statistics associated with polarization speckle including the 1st order statistical statistics of the Stokes parameters and the ensemble-average Van Cittert-Zernike theorem for the ensembled-average generalized Stokes parameters are investigated theoretically and experimentally to demonstrate their link and different physical features as compared with the conventional concepts.