Lehnerus, the kernel is the core of the OS, and in the almost year I've
been using my current Linux Distro (Zorin OS 5) I've seen on kernel patch and a kernel upgrade.
As to Windows patches for apps, the Windows patches usually include patches for MS Internet Explorer, MS Office, .NET, the relevant GUI, and other MS apps - none of which are actual OS patches, although some will claim the MSIE and the GUI ones are since MS have placed them inside the OS security perimeter instead of where they should be outside it.