What is Linux
Linux is a free, <Open Source> operating system for PCs. Its strength comes from a number of major companies who specialize in Open Source and who constantly produce up-to-date, out-of-the-box versions of Linux.
Though Linux is available  under several variations, they all share the same Kernel—the core of the system upon which more advanced features are built, like visual interfaces, programs, the feel-and-look of the system, etc.. This makes Linux-based products portable from variant to variant despite the system's versatility.
Linux is considered a fast, stable, and secure operating system. In the past, using the Linux operating system required at least some knowledge of C programming, which deterred many non-technical users. Today, Linux's sports a beautiful visual interface that runs quickly and smoothly, and easily challenges that of Windows OS.
Popular Linux distribution suites include Red Hat, OpenSUSE, Ubuntu, and Knoppix. All distributions can be downloaded from the Internet and used for free.
Linux in the hosting world
You don't need to know a word of C programming language in order to enjoy the benefits of Linux hosting, nor do you need to have Linux installed on your own local machine.
Because of its stability and because it naturally incorporates server abilities, Linux is the most common hosting platform today. The fact that the operating system and all its applications are free allows Linux hosting providers to offer highly competitive prices.
Linux is also the capital of <Open Source>. Linux servers almost always come with <PHP> support and <MySQL> databases, also an Open Source project. This combination, in turn, allows you use a wide range of free, Open Source Internet applications, from <Content Management Systems> to complete Ecommerce solutions.