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

source package

    A collection (usually an archive file) containing
   all the files necessary to build and modify a piece of
   software.

   A Debian source package includes the original source archive
   (.orig.tar.gz), Debianisation diffs
   (-.diff.gz) and a Debian source control file
   (-.dsc).

   (2000-05-31)