OCCT for Windows refers to the

Open CASCADE Technology (OCCT)

software library running on the Microsoft Windows operating system.

OCCT is a powerful and widely used 3D modeling kernel. It provides a comprehensive set of tools and functionalities for creating, manipulating, and visualizing 3D shapes. Think of it as the engine behind many CAD (Computer-Aided Design) and CAE (Computer-Aided Engineering) applications. The Windows version simply means the library has been compiled and is suitable for use within Windows-based applications.

In short, if you[SQ]re developing a 3D modeling application for Windows, OCCT provides the low-level functionality to handle the complex geometric computations.