old thread, but it means registering the app via the internal (android) package management system as inactive (disabled).
technically this is done by running shell command 'pm disable <package.name>'. pm will then check if the package is present, and if it is, force stop the app and mark the app completely inactive. all packages are managed by the package manager, so if package manager marks an app as inactive then the app cannot be run. however, since the app is still installed (validly) it can be found when sought by other apps, etc. and will be listed if you or an another app fetches a list of installed packages.
this is not like renaming the apk. renaming the apk will prevent the apk from being recognized by android, and that app is uninstalled completely. when you populate a list for all installed packages, it will not appear in this case.
generally it is safer to freeze(disable) the app, since it is done at user level and does not involve a write action on /system. when you factory reset your device the package database will be reset, and your app will be alive again.