C# preprocessor directives

1. #define #undef
#define UNITY_DEBUG 
It tells the compiler that a symbol with the given name exists, in this case UNITY_DEBUG.

#undef UNITY_DEBUG 
does the opposite - it removes the definition of the symbol:

Note:
The #define and #undef commands must be placed at the beginning of the C# source file, before the code declaring any objects to be compiled. (before using)