C/C++ is a mythical programming language that in spite of its nonexistence is nonetheless frequently chosen for software projects.
The term 'C/C++' can be legitimately used to refer to a codebase that includes both CeeLanguage and CeePlusPlus source or code that is both valid C and valid C++, or perhaps a toolset that includes both C and C++ compilers. It's also acceptable for indicating skill required or possessed, as in a job requirement or on a résumé.
The erroneous usage is to suggest that there is a single language known as C/C++. There is not.
-- JoshuaJuran
Not to be confused with ObjectiveCeePlusPlus. This is ObjectiveCee and CeePlusPlus mixed in the same source files, as supported by the GnuCompilerCollection and Apple specifically.
See CeeAitch (Ch) for implementation as an interpreter.
See also CeeAndCeePlusPlusComparedToOtherLanguages CeePlusPlusRoadMap (for both C and C++)