Bucky bit
From Computer History Wiki
A bucky bit is a bit set to indicate a modifier key was pressed. The bucky bits are usually sent along with the key that was modified.
Examples
Some text terminals, and some terminal emulators, has a meta key to set the most significant bit of the key code that is sent to the host.
X11 has eight bucky bits: Shift, Lock, Control, Mod1, Mod2, Mod3, Mod4, and Mod5.
On ITS, a character read from a terminal open in %TOFCI mode has four bucky bits: control, meta, super, and top. The closely related SUPDUP protocol has a subset: the super bit is not included.
