Linux is an operating system -- very much like UNIX -- that has become very popular over the last several years.
Linux is, in simplest terms, an operating system. It is the software on a computer that enables applications and the computer operator to access the devices on the computer to perform desired functions. The operating system (OS) relays instructions from an application to, for instance, the computer's processor. The processor performs the instructed task, then sends the results back to the application via the operating system.
Why Use Linux
Linux comes with a complete development environment, including C, C++, Fortran compilers, toolkits such as Qt and scripting languages such as Perl, Awk and sed. A C compiler for Windows alone would set you back hundreds of dollars.
Security - Well-done administration of a computer with Linux allows for a very secure multi-user workstation.
Viruses are less of a threat now. The system setup of a Linux system does not allow a virus to act as it does on a Windows machine, and the fact that almost no viruses have been written for Linux allows for a very secure feeling.
Excellent networking facilities: allowing you to share CPUs, share modems etc.
Supports multiple processors as standard.
True multi-tasking; the ability to run more than one program at the same time.