Linux is a Free and Open Source Operating System kernel. The project was originally started by Linus Torvalds and now has a very large community of developers and users all around the world. Linux is used in an extremely wide variety of devices such as industrial embedded systems, appliances, smart phones, cell phones (not just Android phones), desktop systems, servers, supercomputers and mainframes. Unix-like operating systems utilizing the Linux kernel are generally referred to as Linux systems although most Linux systems are a combination of the Linux kernel, GNU Utilities, and other software libraries and Open Source projects. As such, the term GNU/Linux is often used to show the combination of the Linux kernel and GNU project. EMAC develops an embedded Linux distribution and supports Linux on nearly every system offered.
If you are new to Linux, the following sites may provide some useful background information: