what is a preprocessor || preprocessor directives

what is a preprocessor :

Preprocessor is a program which runs before the compilation. Preprocessor is not a part of compiler but it is a step executed before the source code is compiled. All preprocessor command start with a symbol of (#).# is called Preprocessor directive and the word after # is called Preprocessor command.

preprocessor directives :

Preprocessor directives are traces covered in a application that being with the person #, which cause them to different from an ordinary source code text. They are invoked through the compiler to process a few programs before compilation. Preprocessor directives trade the text of the supply code and the end result is a brand new source code with out those directives.