implementation [[ISO/IEC 9899-1999]]
particular set of software, running in a particular translation environment under particular control options, that performs translation of programs for, and supports execution of functions in, a particular execution environment
implementation-defined behavior [[ISO/IEC 9899-1999]]
Unspecified behavior where each implementation documents how the choice is made.
locale-specific behavior [[ISO/IEC 9899-1999]]
Behavior that depends on local conventions of nationality, culture, and language that each implementation documents.
undefined behavior [[ISO/IEC 9899-1999]]
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 [[ISO/IEC 9899-1999]]
Behavior where the standard provides two or more possibilities and imposes no further requirements on which is chosen in any instance.