The Free On-line Dictionary of Computing (30 December 2018):

partitioned data set

    (PDS) A data set on an IBM mainframe that
   contains members, each of which acts like a separate data set.
   Partitioned data sets are more space-efficient than individual
   data sets, because they can put more than one data set on a
   track.  They are also used to hold libraries, with one
   function per member.  The syntax for a member is
   NAME.OF.PDS(MEMBER) although some systems (such as Phoenix)
   could use NAME.OF.PDS:MEMBER

   Original PDSes were of fixed size, and needed frequent
   compression to recover space after deleting or changing
   members.  Newer PDS/E Extended PDSes do not have this problem.

   (2003-12-05)