in D3D12Fullscreen they 2 command lists one called Scene the other post

so what is scene and post and their responsibility.

    ComPtr<ID3D12GraphicsCommandList> m_sceneCommandList;
    ComPtr<ID3D12GraphicsCommandList> m_postCommandList;
    ComPtr<ID3D12CommandAllocator> m_sceneCommandAllocators[FrameCount];
    ComPtr<ID3D12CommandAllocator> m_postCommandAllocators[FrameCount];
    ComPtr<ID3D12RootSignature> m_sceneRootSignature;
    ComPtr<ID3D12RootSignature> m_postRootSignature;
    ComPtr<ID3D12PipelineState> m_scenePipelineState;
    ComPtr<ID3D12PipelineState> m_postPipelineState;

I am trying to follow DirectX tutorials using DR template DirectXTK12 it's well written unlike directx12 samples because there's inconsistency in directx12 sample.

What I want to do is to implement the two command lists in DeviceResource template but first I need to understand that concept, I already tried to look at other samples but i got confused even more

so can someone explain what is scene and post are or point me to an article or a book that explains it.