What a Linux Distribution Is:-
To understand what a Linux distribution is, it is necessary to first explain what Linux is and a little about its component parts. This involves the component parts of an operating system (OS) including such things as file systems. This article will attempt to explain these concepts at a basic level.

What is an Operating System?
An operating system consists primarily of three things:
1.A filesystem - All the files that run and support an operating system along with other files must reside on a filesystem.
2.One or more core programs - The program that provides all the basic support is included here. Sometimes an operating system is split into programs performing various uses.
3.Other support programs - In the DOS operating system, there were various support programs that enhanced a users ability to perform tasks, but they were fundamentally important for the use and versatility of the operating system. One of these programs included a disk format program.
Beyond this, other specific programs would provide additional functionality to the operating system.

What is Linux?   
Linux is an operating system which is built from various packages. The various packages provide various functions to the system. Sometimes these functions are critical to the ability of the operating system to run, and sometimes they are not.Linux software basically consists of:-

1.A kernel - This is the central or core program of the operating system. It provides support for interfacing to all devices such as the keyboard, monitor, network devices, and other devices.
2.Support programs for the kernel - These programs allow the system or user to manage the kernel and allows the loading and unloading of modules in the kernel
3.The shell program - This the program that interprets user commands and acts on them. Linux provides choices of several shell programs. Each shell program may be a separate "Linux package".
4.Programs that support and add enhancements to the operating system with regard to functions like logging in.
5.Server programs - Programs that provide specific network services, either on the client and/or the server side.

What is a Linux Package?
A Linux package consists of a package of one or more programs with associated documentation that will perform a specific function either for the operating system or add additional capabilities such as providing a web server. (The Apache web server package). Sometimes the source code is included as a part ot the package. There are a few package types.
What is a Linux Distribution?
It is obvious by now that a Linux distribution is in a basic sense a set of packages that together make up the operating system.In order to install the operating system the tools to perform the install must be available in the correct order for the user. A user interface must provide information to the user so they will know what they can do and what their choices are.

Various distributions will allow: -
1.    Different tools and methods to set the system up.
2.    Different choices with regard to setup.
3.    Various choices of packages to install. 
The core of the operating system is still likely to be the same or similar and many of the packages used will be the same. Also the user can get additional packages and install them on the operating system. Some General Linux Distros are Ubuntu,Redhat,CentOS,Debian,Fedora and many more.
Linux Distro Chart:-

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