Linux is a Unix-like computer operating system assembled under the model of free and open-source software development and distribution. The defining component of Linux is the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds.
What is "Open Source?": Open source simply means that the source code for the piece of software is available to the public. Open Source follows a few key philosophies.
The freedom to run the program, for any purpose.
The freedom to study how the program works, and change it to make it do what you wish.
The freedom to redistribute copies so you can help your neighbor.
The freedom to distribute copies of your modified versions to others.
What is a distro?: A Linux distro (short for distribution) is a collection of packages to make a working operating system. Ubuntu is a good example of a distro that gives users a full operating system. Distros are comprised of several different pieces of software, each of them having their own importance to the system.
Some components of a Linux distro: Kernel, Bootloader, Display Manager, Display Server, Desktop Environment, Window Manager, Daemons, Shell, Applications/Utilities. These are just several pieces of many that a Linux distribution can contain.
What are some uses of Linux? There are many uses of Linux ranging from desktop use with distros like Ubuntu, Fedora, and Elementary to server use with distros like Cent OS, Redhat, and Ubuntu. In recent years Linux and Other alternative operating systems such as FreeBSD have made their way to the public eye in devices such as the Steam Machine, which runs a variation of Debian. Devices such as the PS4 and Nintendo Switch run on a variation of the FreeBSD kernel.
I'm convinced I now need to install a Linux distro! Well before you jump the gun and dump your current operating system for a Linux distribution it is recommended that you try out a few distributions inside of a virtual machine.
Popular Distributions: There are literally thousands of distributions ranging from something original to a fork of another distribution. Here is a decent list of the most popular distributions within the last 30 days pulled from DistroWatch.
Kernel: The is the core to the operating system. Without this you aren't going to be able to do anything as it manages the CPU, memory, and peripheral devices.
Bootloader: A piece of software that manages how you boot into your OS. GRUB is one of the more popular bootloaders out there.
Display Manager: A display manager otherwise known as a login manager is an application that opens at the end of the boot process. They ususally allow the user to login and pick which Desktop Environment or Window Manager they want to use.
Display Server: A sub-system that displays the graphics onto your monitor it is also known as X Sever or just X. Popular display servers include Xorg/X11, Wayland, and Mir.
Desktop Environment: A desktop environment is what users interact with. Think Windows Desktop. Well known DE's include GNOME, Unity, KDE, etc the list can go on.
Window Manager: A window manager is like a Desktop Environment however it is slimmed down and typically used to just manage window placement and space. There are several types of Window Managers ranging from Tiling WM's to Freeform WM's. Tiling WM's tile your windows so no space is wasted, where as Freeform WM's let you place your windows in any way.
Daemons: A daemon is simply put a background task. Windows users often call them Services.
Shell: A shell is a command line that lets you send commands directly to the system instead of clicking through an interface. There are different types of Shells, however the most common is BASH. Others include ZSH, Fish.
Applications/Utilities: These are what you use on your computer. They can range from a web browser like Firefox to an office suite software like Libre Office Calc.
What I use:
I use Arch Linux with i3wm as my Window manager and GDM as my display manager. Here is a beautiful screenshot of my old laptop setup.