4.4.4 Changing the action of the shifted arrow keys

This option affects the arrow keys, if you press one with any of the modifier keys Shift, Ctrl or Alt held down.

• In the default mode, labelled Ctrl toggles app mode, the Ctrl key toggles between the default arrow-key sequences like ESC [A and ESC [B, and the sequences Digital's terminals generate in ‘application cursor keys’ mode, i.e. ESC O A and so on. Shift and Alt have no effect.
• In the ‘xterm-style bitmap’ mode, Shift, Ctrl and Alt all generate different sequences, with a number indicating which set of modifiers is active.

If you don't know what any of this means, you probably don't need to fiddle with it.