This option allows choosing the operating system which should be selected when booting. By default this always is the first one. This option means that the default entry selection stays the same when placing other operating systems there.
In contrast to the first option the other choices are referenced by name. So the default system isn't changed when moving to another position.
If you want to use another reference like "always point to the second entry" you can use the last option which allows typing a custom reference. Usage examples:
1 = "always point to the second entry" (counting starts by 0)
test>0 = "always point to the first entry of a submenu named test"
