An NPY file (NumPy Array File) is a standard binary file format used to store numerical data, specifically NumPy arrays, which are the fundamental data structure in the NumPy library for Python. NumPy arrays are highly optimized for numerical operations and are widely used in scientific computing, data analysis, machine learning, and artificial intelligence. The NPY format allows for efficient serialization and deserialization of these arrays, preserving all array metadata, including its shape, data type (dtype), and whether the array is Fortran-contiguous or C-contiguous. This ensures that when an NPY file is loaded, the array is reconstructed exactly as it was saved, maintaining data integrity and precision. Unlike plain text formats like CSV, NPY files are binary, which makes them much faster to read and write, especially for large datasets, and they consume less disk space. They are particularly useful for saving intermediate results of computations, sharing datasets between different Python scripts or projects, and for persistent storage of model weights or feature sets in machine learning workflows. While primarily associated with Python and NumPy, the simplicity and efficiency of the format make it a de facto standard for exchanging numerical data within the Python scientific ecosystem.