Shapes (or colliders) define the form of an object for collision detection.
These have the fast and simple collision algorithms and are the best to use if possible.
This is made up of multiple primitives called child shapes. Each child can have its own local transform. For example, a table can be created with a box for the surface and four cylinders for the legs.
A plane split the world in two half spaces and objects with collide with it from one side.