Linux is a complete operating system that is similar but not identical to Unix. It runs on a wide variety of hardware, ranging from Intel and AMD CPUs to more exotic hardware such as Digital Alpha computers, PowerPCs, and Silicon Graphics workstations. Probably the most unique characteristic of Linux is that it is freely distributable. Freely distributable means that the source code for the kernel and most software cannot be withheld. It does not mean that companies cannot charge for it. By means of comparison, hosting a website on Unix or Linux is nearly identical.
Unix is a computer operating system. Unix was created in the late 1960s, in an effort to provide a multi-user, multitasking system. The philosophy behind the design of Unix was to provide simple, yet powerful utilities that could be pieced together in a flexible manner to perform a wide variety of tasks.