A call stack entry used as the point to which control is transferred when an unmonitored error occurs or a high-level language termination verb is used. A control boundary can be either of the following: a) any Integrated Language Environment (ILE) call stack entry for which the immediately preceding call stack entry is in a different activation group, or b) any ILE call stack entry for which the immediately preceding call stack entry is an original programme model (OPM) program.