The Off-Canvas Settings deal with the off-canvas menu part of the theme. This setting will only appear if you have selected Off-Canvas in the Menu Selection section.
There is only one setting in this section, Change hamburger icon text. This allows you to change the default text that appears next to the hamburger icon itself. This is another area of the customizer that will update automatically when you change it. This means that once you start typing you will see the changes in real-time to the right: