A CMake file is a plain-text script used by the CMake build system, a cross-platform tool designed to control the software compilation process using simple platform and compiler-independent configuration files. These files, typically named 'CMakeLists.txt' or ending in the '.cmake' extension, contain a series of commands that define how a project should be built, including source file locations, dependencies, compiler flags, and installation rules. By using these scripts, developers can generate native build files such as Makefiles, Ninja build files, or project files for IDEs like Visual Studio and Xcode. This abstraction allows a single codebase to be compiled across various operating systems and environments without requiring manual configuration for each platform. The language used within these files is a domain-specific language that supports variables, loops, conditionals, and modular functions, making it highly flexible for managing complex software projects ranging from small libraries to massive enterprise applications.