A flag on some processors indicating an attempt to calculate a result too large for the destination register to hold.
More generally, an indication of any kind of capacity overload condition. "Well, the Ada description was baroque all right, but I could hack it OK until they got to the exception handling ... that set my overflow bit."
The hypothetical bit that will be set if a hacker doesn't get to make a trip to the Room of Porcelain Fixtures: "I'd better process an internal interrupt before the overflow bit gets set".
This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)