A .lib file is a static library file format, primarily used on Windows systems. It contains pre-compiled code, routines, functions, and data that can be linked into a program during the compilation process. Unlike dynamic libraries (DLLs), the code from a static library is copied directly into the executable file during linking. This means that the resulting executable is self-contained and does not rely on external library files being present on the system at runtime. Static libraries are often used to distribute reusable code components, such as mathematical functions, data structures, or GUI elements. They offer the advantage of simplifying deployment, as all necessary code is embedded within the executable. However, they can also lead to larger executable sizes and potential code duplication if the same library is used by multiple programs. When a program is compiled, the linker resolves references to functions and data within the static library and incorporates the corresponding code into the final executable. This process creates a single, independent executable file that can be run without requiring the presence of the .lib file itself.