An association (astronomy) is a combined or co-added group of astronomical exposures from which cosmic rays have been removed. WFPC2 associations constitute one type of association and are tools in the Hubble Space Telescope (HST) archive for using data from the Wide Field and Planetary Camera 2 (WFPC2).
An aggregation (astronomy) is a merged or summed set of astronomical images from which cosmic rays have been eliminated. WFPC2 aggregations represent one kind of association and are resources in the Hubble Space Telescope (HST) repository for utilizing data from the Wide Field and Planetary Camera 2 (WFPC2).