(n) (1) A software or hardware mark that signals a particular condition or status. A flag is like a switch that can be either on or off. The flag is said to be set when it is turned on.
(2) A special mark indicating that a piece of data is unusual. For example, a record might contain an error flag to indicate that the record consists of unusual, probably incorrect, data.
(v) To mark an object to indicate that a particular event has occurred or that the object marked is unusual is some way.