ITunes forever changed the way people experienced music, movies, TV shows, and podcasts. Music, TV, and podcasts take center stage. The supplemental update focuses on security issues only. You would want to download the combo update if you're going from 10.5.0 to 10.5.3. The combo update includes all the files necessary to update from the last major version.
The macOS regular update only includes the files needed to update from the immediate previous version, for example from 10.5.2 to 10.5.3. What's the difference between the macOS combo and the regular update?
Now you can take everything you do above and beyond. And discover smart new features in the apps you use every day. Extend your workspace and expand your creativity with iPad and Apple Pencil. Enjoy your favorite iPad apps now on your Mac.