For questions about the "super" modifier key, which is usually Mod4 in X11. On many systems, this is a key labelled with or .
Keypresses in X have 8 modifier bits: Shift, Lock, Control, Mod1, Mod2, Mod3, Mod4, Mod5.
Meta, Super, and Hyper are all keys from the old Symbolics keyboard for which X still has internal keycodes, so they can still be bound to modifiers. On modern keyboards, Super is the 
/Tux/whatever key next to Alt. It's usually bound to Mod4.
