A Static Rigidbody 2D is designed to not move under simulation at all. If anything collides with it, a Static Rigidbody 2D behaves like an immovable object (as though it has infinite mass). It is also the least resource intensive . A Static body only collides with Dynamic Rigidbody 2Ds.

Aside from setting the Rigidbody 2D to the Static Body Type, there is another scenario where a Static Rigidbody 2D is created. This is when a GameObject with a Collider 2D component does not have a Rigidbody 2D component at all. All Collider 2Ds without a Rigidbody 2D component are internally considered to be attached to a single hidden Static Rigidbody 2D component.

This means that you are able to create a large number of Static Collider 2Ds as you do not have to add a Rigidbody 2D component for each individual GameObject. Both methods of creating Static Collider 2Ds have their advantages, depending on the scenario.

If an individual Static Collider 2D needs to be moved or reconfigured at runtime, then add a Rigidbody 2D component and set it to the Static Body Type, as it is faster to simulate the Collider 2D when it has its own Rigidbody 2D. If a group of Collider 2Ds needs to be moved or reconfigured at runtime, it is faster to have them all be children of the single hidden parent Rigidbody 2D than to move each GameObject individually.