TLDR: a Linux distribution is a collection of software including the Linux kernel that is provided to users via the Internet.
In this post I’m going to explain what the phrase “Linux Distribution” means. I’m assuming a basic level of competence with technology, but not necessarily anything in depth. I will make prolific use of links to Wikipedia and other websites where appropriate. I am not attempting to advocate anything, just explain, but I have some personal bias as a Linux user.
First, the more important question is “What is Linux?”
This is a surprisingly multi-faceted and multi-layered question, and the answer will depend on who you ask. In its most inarguable and basic form, Linux is a kernel originally designed by a programmer named Linus Torvalds. Yes, go ahead and read the Wikipedia article on kernel, it will be important for deeper understanding of the rest of the article.
For those who do not want to read Wikipedia, I will paraphrase. A computing kernel is the core software that connects the hardware (like your mouse and keyboard) to the applications (like Unreal Tournament or Google Chrome).
The more complex answer to the question of “What is Linux” comes with regards to the common use of the word which often includes things other than just the kernel. According to some people (especially Richard Stallman), the word “Linux” should not refer to anything other than the kernel, but those people do not control the way people use language, and quite a lot of people lump other meaning into the word.
Let’s go ahead and skip to the next word, “distribution”, so as to avoid getting lost in a battle of semantics that’s been raging for the past 20 years. Typically distribution refers to the aspect of sales where a product is transported from factory to consumers, or from factory to merchant. Linux and the accompanying software is predominately a product free of charge and so the “sales” and “merchant” aspects are ignored. It remains however that distribution in this case refers to the transportation of the product from factory to consumer (or perhaps “user” is the better term).
This leaves two important questions: What is the product? and also What is the means of transportation?
The sales metaphor is a little weak because it comes from a past of material analog objects. Linux distributions are primarily digital software objects. The product is a collection of software applications including the Linux kernel which can be used as a computer operating system, or OS for short. You might be familiar with the term, or at least the abbreviation from “Mac OSX”. That basically means Mac operating system number 10 (X is the roman numeral for 10). Suffice it to say however, that Mac OS X is not a Linux distribution because it does not include the Linux kernel. That is the fundamental requirement for something to be considered a distribution of Linux: the inclusion of the Linux kernel.
Most Linux distributions can be used similarly to Mac OS X, or Windows, but this is not a requisite to be included in the definition of a Linux distribution. Many Linux distributions (or distros for short) are meant to run on servers, routers, firewalls, e-readers, et cetera.
Now, more on “distribution” within the framework of a means of transportation. Most Linux distributions provide their software bundles (including the Linux kernel) from a website or a file server somewhere. People can then download them to their personal computers over the Internet or a network. Some Linux distributions sell CDs or DVDs with the same bundles on them, especially for people who have slow network connections.
Once installed onto a computer, the idea of transportation remains relevant in a way that may not be familiar to users of Windows or Mac OS. Because Linux distros bundle primarily free of charge software, they want their users to have easy access to it whenever the user needs it. To fill that need most distributions have developed digital packaging systems. For contrast, in the old days users got new software for Windows by going to the store, buying it, popping out the CD, and installing it. You can think of packaging systems as free of charge “App Stores” if you’re familiar with modern smart phones and tablets. The idea for these stores was taken directly from the packaging systems of Linux distros.
These packaging systems help move software, like new versions of the Linux kernel or Firefox, from the factory (being programmers in this case), to the users, via the Internet. Specifically most distributions offer carefully monitored package repositories for this specific purpose. The advantaged to monitored package repositories is that viruses and malware are much harder to embed because the community is pre-screening the applications before they’re made available to users. Compare this to downloading files from an unmonitored, third-party website like warez sites.
So, in short, a Linux distribution is a collection of software including the Linux kernel that is provided to users via the Internet.