This is a feature of the WinDriver tool-kit that allows you to develop a kernel-mode driver and move performance-critical sections of your code (such as interrupts acknowledgment and handling) from the user mode to the kernel mode.
For detailed information about the Kernel PlugIn feature, refer to the WinDriver PCI User’s Manual.

Beginning with version 6.0 of WinDriver, the Kernel PlugIn does not support the USB API. However, USB development does not generally require this feature.