Weight images are variance maps. For single epoch PS1 Warp images, these variance contains the readnoise, Poisson noise, and other noise sources. For PS1 Stack Images, the noise is propagated from the individual input warps. These weight images can be used for estimates of the uncertainties in the photometry. We note that the deprojection of the chip images into the warps correlates the pixels, introducing covariance. Therefore the derived uncertainties might underestimate the true noise.
The starting point for the PS1 data archive is at The Pan-STARRS1 data archive home page.
The following information is taken from Waters et al., which should be cited appropriately.