Packages are sets of files created by a site administrator.
Emilio Lazardo belongs to the Sales and Mktg groups. Penny Priddy belongs to the Tech group. If the administrator makes a package available to the Sales group, both Emilio and Lazardo have access to the package. If a package is made available to the Tech group, John and Penny both have access to the package. If a package is made available to both Tech and Mktg, then all three have access to the package.