A PackageImport is a DirectedRelationship between an importing Namespace and a Package, indicating that the importing Namespace adds the names of the members of the Package to its own Namespace.
Conceptually, a Package import is equivalent to having an ElementImport to each individual member of the imported Namespace, unless there is a separately-defined ElementImport. If there is an ElementImport for an Element, then this takes precedence over a potential import of the same Element through a PackageImport.
Relates
The Package Import relationship can be drawn like this: