The VTK (Visualization Toolkit) file format is a legacy data format used primarily for 3D computer graphics, image processing, and scientific visualization. Developed as part of the open-source Visualization Toolkit software system, this format is designed to represent a wide variety of dataset types, including structured points, rectilinear grids, structured grids, unstructured grids, and polygonal data. A standard VTK file consists of five main sections: the file version and identifier, a header containing a title or description, the file format type (specifying either ASCII or binary), the dataset structure which defines the geometry and topology, and finally the data attributes which store values like scalars, vectors, tensors, or texture coordinates associated with the points or cells. While the legacy VTK format is still widely used due to its simplicity and broad support in the scientific community, it has largely been superseded by newer XML-based VTK formats (such as .vtu or .vtp) which offer better support for parallel processing, compressed data, and random access. It remains a staple in academic and engineering fields for sharing simulation results and complex geometric models.