2D joints are the 2D counterparts of the 3D joint physics components, and are made to work only with 2D GameObjects. You can only attach 2D joints to GameObjects which have an attached Rigidbody 2D component, or to a fixed position in world space. A 2D joint connects a Rigidbody 2D GameObject to another Rigidbody 2D GameObject. 2D joints can apply forces that move Rigidbody GameObjects, and joint limits can restrict that movement.
You can tell a 2D joint from its 3D counterpart in the Component browser by its name ending in ‘2D’.
There are many different types of 2D joints available. Refer to each joint’s respective page for detailed information about their properties and uses. These can be found in the 2D Joints section.