The term “combo update” is generally used to mean a combined set of updates within the context of a 10.x version. So for example the 10.13.6 combo updater can be used to update any of the 10.13.y releases. This is what the App Store will use if you are more than one update out of date otherwise it uses a differential update that will be a smaller download & less complicated.
Troubleshooting problems with macOS may see a recommendation given to run the combo updater. The reasoning behind this is generally that it performs a refresh of more of the operating system files than a differential update, but fewer (ie. faster) than a full reinstall. For support consultants the combo updater is a useful file to have on hand to be able to update the Macs of clients without the whims of slow or missing internet connections.
There is no combo download to perform an upgrade. For these the naming is an “installer”. If you download the installer via the App Store it can be “burned” onto a thumb drive to make an installer that will work on all eligible hardware.
This post was modified 7 months ago by Graham McKay