Linux is an Operating System, which acts as a communication service between the hardware (or physical equipment of a computer) and the software (or applications which use the hardware) of a computer system.
Multitasking (a technique for sharing a single processor between several independent jobs)
Virtual Memory (allows repetitive, extended use of the computer's RAM for performance enhancement)
Fast TCP/IP Drivers (for speedy communication)
Shared Libraries (enable applications to share common code)
Multi-user Capability (this means hundreds of people can use the computer at the same time, either over a network, the Internet, or on laptops/computers or terminals connected to the serial ports of those computers).
Protected Mode (allows programs to access physical memory, and protects stability of the system)