This section describes the main components available through Unity’s built-in 3D physics engineA system that simulates aspects of physical systems so that objects can accelerate correctly and be affected by collisions, gravity and other forces. More info
See in Glossary, which you can use in object-oriented projects. It includes the following:
In addition, the 3D Physics Reference provides a detailed description of all available components and the Physics HOWTOs section contains a few tips about common physics-related tasks.