What is a "Dynamic Mesh Element"?

This question is not necessarily related to VR development and I posted it to the engine source forum last week but didn’t get any answer. Can anyone here help me understand what a “Dynamic Mesh Element” is?

The base pass rendering in deferred rendering consists of rendering static meshes (RenderBasePassStaticData) and RenderBasePassDynamicData. I cannot figure out what is being rendered in “RenderBasePassDynamicData”? What will qualify as dynamic data? How dynamic meshes are different from static meshes?

I looked into it more and my understanding is that all other render-able geometry other than static meshes are rendered in the dynamic data pass. It includes skeletal meshes, hierarchical instanced static meshes, etc.