The following describes the application object layers in Microsoft Dynamics 365:
USR - The user layer is for user modifications, such as reports.
CUS - The customer layer is for modifications that are specific to a company.
VAR - Value Added Resellers (VAR) can make modifications or new developments to the VAR layer as specified by the customers or as a strategy for creating an industry-specific solution.
ISV - When an Independent Software Vendor (ISV) creates its own solution, its modifications are saved in the ISV layer.
SLN - The solution layer is used by distributors to implement vertical partner solutions.
FPK - The FPK layer is an application object patch layer reserved by Microsoft for future patching or other updates. For more information, see Patch Layers.
GLS - When the application is modified to match country or region-specific legal demands, these modifications are saved in the GLS layer.
SYS - The standard application is implemented at the lowest level, the SYS layer. The application objects in the standard application can never be deleted.