implementation-defined behavior
Unspecified behavior where each implementation documents how the choice is made.
locale-specific behavior
Behavior that depends on local conventions of nationality, culture, and language that each implementation documents.
undefined behavior
Behavior, upon use of a nonportable or erroneous program construct or of erroneous data, for which the standard imposes no requirements. An example of undefined behavior is the behavior on integer overflow.
unspecified behavior
Behavior where the standard provides two or more possibilities and imposes no further requirements on which is chosen in any instance.