In .NET Framework, a constrained execution region (CER) defines an area in which the common language runtime (CLR) is constrained from throwing out-of-band exceptions that would prevent the code in the area from executing in its entirety.
A constrained execution region (CER) is part of a mechanism for authoring reliable managed code. A CER defines an area in which the common language runtime (CLR) is constrained from throwing out-of-band exceptions that would prevent the code in the area from executing in its entirety. Within that region, user code is constrained from executing code that would result in the throwing of out-of-band exceptions. (Excerpt from the MSDN library)
