A full Linux distribution and a computer running it, require many ingredients besides just the Linux kernel. However, the word Linux is often sloppy applied to the entire system. In fact, a more restricted use is just to describe the kernel of the operating system, which is the component that connects the hardware to the software, and manages resources such as memory, CPU, time sharing, etc. You can have a system which runs only a kernel, without all this additional functionality, and that appears sometimes in embedded devices for appliances. In addition to the basic kernel, the operating system has to include important system libraries. Usually, these are shared libraries or dynamic linked libraries that can be used by more than one program at a time without wasting more memory, and the most important one is libc. Almost every application uses libc. Then, there are all sorts of system services or applications that often run in the background waiting for a task to be done. These are often called daemons. Basic system utilities that are used every day by system administrators includes those which let you look at files, view them, edit them, rename them, remove them, that lets you bring network connections up and down, etc. Many of these utilities are used by the services we already discussed. One particularly important program is the command shell program, which is what you are using when you're working at the "command line". The most common one and the default one for Linux is called bash, which stands for Bourne Again Shell. So here's a picture of the main components of the operating system, starting from the hardware, up to the kernel, basic libraries, and device drivers, etc., and then showing on top of that, both the graphical interface and some of the most important applications, such as tools used by applications, such as Apache, etc. Now, most users on a desktop or laptop will be using a graphical user interface or GUI. Traditionally, Linux systems all used the X Windows system, often just called X. It's been around since at least 1984, but that only does the very low-level operations needed to run a graphical interface. On top of that, there has to be a window manager which controls the actual behavior of windows and their appearance, and on top of that even a desktop manager that controls the entire desktop, and that's what the user really feels the most common choices in Linux are GNOME and KDE. However, these days, many systems are starting to move over to what's called a Wayland, instead of X. So, in addition to that, there are many applications that come with the standard installation. They're not strictly part of the operating system, they are added in with the Linux distribution. That includes browsers and many basic utility programs. There's a lot of choice for these components in Linux. They're used in a very modular way and so, even on a given Linux distribution, different users can have a quite different experience, depending on what kind of choices they make. Also, many developer tools are supplied quite easily on any Linux distribution. These include compilers, debuggers, etc. They're not additional software that has to be paid for or installed, they are always available on all Linux distributions. A Linux distribution itself brings all these ingredients together in a coherent way, makes sure all the different parts work together, that if different choices were made, they will still work together, etc. So, even if all the ingredients are sort of the same, they can feel quite different when built together in a Linux distribution, since there are so many choices. So, that's a brief discussion of the distinction between Linux, and the Kernel, and the Operating System, and some of the other ingredients that must go into a full system.
