GNU Build System is a collection of tools and procedures used to manage the process of building and distributing software packages. It includes the GNU Compiler Collection (GCC), GNU Autoconf, GNU Automake, and GNU Libtool, among other tools. The system provides a consistent and portable way to compile, configure, and install software on a variety of platforms, making it easier for developers to create software that can be easily distributed and installed on a wide range of systems. It is a specialized skill that requires knowledge of these tools and the ability to use them effectively.