This is the subscript for the LNEXT character in the special control
character array. termios.c_cc[VLNEXT]
holds the character
itself.
The LNEXT character is recognized only when IEXTEN
is set, but in
both canonical and noncanonical mode. It disables any special
significance of the next character the user types. Even if the
character would normally perform some editing function or generate a
signal, it is read as a plain character. This is the analogue of the
C-q command in Emacs. “LNEXT” stands for “literal next.”
The LNEXT character is usually C-v.