When we discuss Linux Operating Systems we actually Talk about Whole OS or the Linux Distribution, not just the Kernel. Technically Linux is the Kernel of the OS. A kernel is the core part of any OS which basically handles Hardware. When we use Linux kernel and add other important things like the shell, Various Libraries, GUI and other programs like Multimedia Apps etc. Then we refer that systems as a Linux Distribution which in general can be considered as complete OS. There is there are dozens of Linux distributions available but few of them which are very popular and widely used around the world.
Watch the video below for more details about Linux distributions