3 Terms and definitions [intro.defs]

3.21[defns.erroneous]erroneous behavior

well-defined behavior that the implementation is recommended to diagnose
[Note 1: 
Erroneous behavior is always the consequence of incorrect program code.
Implementations are allowed, but not required, to diagnose it ([intro.compliance.general]).
Evaluation of a constant expression ([expr.const]) never exhibits behavior specified as erroneous in [intro] through [cpp].
— end note]