The bless operator turns the variable pointed to by the reference into an "instance variable" for an object, thus creating an instance of a class, to use the parlance of Java or C++. __PACKAGE__ is a special variable that contains the current package name, so the singleton is an instance of the current package. The idea of a Singleton class is that there should be only one instance of it.

As merlyn has pointed out elsewhere, you don't really need to create an instance at all:

http://www.perlmonks.org/?node_id=183417