The general form is
#define symbolic_constant value
Where symbolic_constant is any valid C or C++ identifier (alphanumeric, first char is alpha, underscore counts as alpha, etc.)
The preprocessor will substitute the value for the symbolic_constant before handing the program to the compiler.
#define jfdklsajfds USHORT
only makes sense if USHORT is known to the compiler by the time jfdklsajfds is used in the program. Then, anywhere you use jfdklsajfds, it is af you had used USHORT
printf("sizeof(x) = %d\n", sizeof(x));