1. Cpp is the GNU C-Compatible Compiler Preprocessor. Cpp is a macroprocessor which is used automatically by the C compiler to transformyour program before actual compilation. It is called a macro processor because it allows you to define macros (abbreviations for longerconstructs). The C preprocessor provides four separate functionalities: the inclusion of header files (files of declarations that can besubstituted into your program); macro expansion (you can define macros and the C preprocessor will replace the macros with their definitions throughout the program); conditional compilation (using specialpreprocessing directives, you can include or exclude parts of the program according to various conditions); and line control (if you use a program to combine or rearrange source files into an intermediate file which is then compiled, you can use line control to inform the compiler about where each source line originated). From Redhat 8.0 RPM

2. The GNU C preprocessor. The GNU C preprocessor is a macro processor that is used automatically by the GNU C compiler to transform programs before actual compilation. This package has been separated from gcc for the benefit of those who require the preprocessor but not the compiler. This is a dependency package providing the default GNU C preprocessor for Debian GNU/Linux systems (version 2.95.4 for architecture i386). From Debian 3.0r0 APT