This is gonna seem like a fuckload of irrelevant CS shit but I swear it will all come together in the end Linux What is Linux? Technically speaking, a kernel CAN be built to only include an IPC (an IPC is what dictates what process to run in what order, and occationally [depending on the design] how memory is alliocated for that particular process).
Side note: A process is a single piece of running code. You can think of it like a thought. A single action (ala picking up something from the ground or deciding where to go to eat) CAN be one thought but is usually many processes that work together interlinked, but that's getting into userspace which I'll cover in a second But more often than not, a kernel includes a lot of other bits to understand what your hardware does (so basic backup graphics/x86 (x86 is a type of CPU that runs a specific set of instruction called x86) drivers, as well as stuff like file system drivers (so in linux one of the options is EXT3, but in Windows you get NTFS - this is HOW the 1s