A flag, usually in hardware, thAT selects between two (usually quite different) modes of operATion. The connotATions are different from flag bit in thAT mode bits are mainly written during a boot or set-up phase, are seldom explicitly read, and seldom change over the lifetime of an ordinary program. The classic example was the EBCDIC-vs.-ASCII bit (#12) of the Program StATus Word of the IBM 360. Another was the bit on a PDP-12 thAT controlled whether it ran the PDP-8 or the LINC instruction set. [Jargon File]