Flag

Definition
A flag is "a 'yes/no' indicator used to represent the current status of something."

Overview
"A flag is often only one bit of the byte and is created and controlled by the programmer in software. When only a single bit] is used, eight flags, or status conditions, can be represented by one [[byte. Flags can also be built into and turned on and off by hardware, in which case the software is used only to read the flag to determine the current condition of the device."

Source

 * PC Encyclopedia, "Flag" (full-text).