Physics components
The Physics engine of Unity works by components. Some describe properties of the object itself, others with respect to each other, or some even within a certain region of the game world.
They can be divided as follows:
Rigidbodies: Which define a rigidbody within the Physics engine
Colliders: Which define a physical shape for the rigidbodies
Joints: Which impose one or more constraints on the rigidbodies
Effectors:Â Which change the physical property in some region of the game world, influencing all the rigidbodies within that region

A summary diagram of the different components of the 2D Physics engine of Unity
Now, let's see them in more detail.