Application Packaging Standard defines the packages structure and rules of packages processing. Package is a file that contains an application files and metadata required to create and manage instances of the application.
Package contains essential information that uniquely identifies each package among others of the same application. Namely, it is application version, package release and packager's signature. For example, if packager changes something in application metadata or in application files, it must be reflected in metadata and signing data. This ensures package consistency and integrity.