Flag, n. Semaphore or indicator of a particular state. The keys on your
computer keyboard are flags in a sense because they can be in more than one
state (depressed or not, up or down) and this difference in states is used
to send signals. MUDs use a similar principle to keep track of what's
happening in all objects. A player might have a flag to indicate whether or
not it is authorized to use builder commands for instance. MUDs also employ
variables.