The .cuh file extension is a specialized header file format used in the NVIDIA CUDA (Compute Unified Device Architecture) programming environment. It is essentially the C++ header equivalent for CUDA-enabled source code. While standard C++ headers use the .h or .hpp extension, the .cuh extension is used to explicitly signal to the NVIDIA CUDA Compiler (NVCC) that the file contains CUDA-specific declarations, such as device kernels, global variables, and host-device functions that utilize the CUDA API. These files are included in .cu source files using the preprocessor directive #include. By separating declarations into .cuh files, developers can maintain modular codebases, share function prototypes across multiple translation units, and ensure that the compiler correctly handles the parallel computing constructs required for GPU acceleration. The format is critical for high-performance computing, deep learning frameworks, and scientific simulations that rely on offloading intensive mathematical computations from the CPU to the GPU.