Unity 3D is a cross-platform game engine used to develop video games for various platforms such as PC, consoles, mobile devices, and virtual reality devices. It provides a user-friendly interface and a wide range of tools and features for game development, including physics, animation, scripting, and asset management. Unity 3D supports multiple programming languages such as C#, JavaScript, and Boo, and allows developers to create 2D and 3D games with ease. It also offers a large community of developers and resources for learning and troubleshooting. Overall, Unity 3D is a powerful and versatile software for game development.