Kernel exclusions (kernelProcessExclusions / kernelFileOpExclusions) are configuration rules applied to the App Control driver component which executes in kernel space. They are used to exclude specific operations processed by the driver by either file type or procedure. Kernel exclusions are ordinarily used for reasons of performance or interoperability with other program.
The exclusion above will tell the Agent to ignore .dll files in the \appdata\local\microsoft\onedrive\* directory.