VTK, or Visualization Toolkit, is an open-source software system designed for 3D computer graphics, image processing, and visualization. It provides a wide range of libraries and tools that are useful for developing scientific and engineering applications that require 3D visualization, such as medical imaging, computational fluid dynamics, and data visualization. The package supports a wide range of visualization algorithms and techniques, including volume rendering, isosurface extraction, contouring, and glyphs. VTK is implemented in C++ with Python bindings, and includes pre-built classes and functions for manipulating and visualizing data. The package has been used in various applications, including medical imaging, computational fluid dynamics, molecular modeling, and geospatial data visualization.