A CPP file is a source code file written in C++, a popular programming language that adds features such as object-oriented programming to C. The file can be a standalone program or one of many files references in a development project. It must be compiled by a C++ compiler for the target platform before run.
CPP files are most commonly edited with programs that provide syntax highlighting. You can still open CPP files using any text editor, but programs that provide syntax highlighting, auto completion, and other helpful tools are most often used.
C++ is one of the most popular programming languages and therefore CPP files are very common.
Common CPP Filenames:
main.cpp - The source code filename typically used for the main() function of a C++ program, where the program begins execution.