1. A variable that serves as an indicator about the stattus of a program or some data. A flag in a database record might be true if the other fields in the record show that a videotape is overdue, for example. From QUECID

2. n. [very common] A variable or quantity that can take on one of two values; a bit, particularly one that is used to indicate one of two outcomes or is used to control which of two things is to be done. "This flag controls whether to clear the screen before printing the message." "The program status word contains several flag bits." Used of humans analogously to bit. See also hidden flag, mode bit. From Jargon Dictionary