Linux is an operating system.
What is an operating system?
A good definition from the Wall Street Journal:
Operating system software is the program that orchestrates all the basic functions of a computer.
— The Wall Street Journal, Tuesday, Sept 15, 1987
I specialize in Linux server systems. They are secure, versatile and cost effective. They can be used as document servers that are compatible with Windows and Mac. They can serve as a VPN to provide encrypted remote access to an office location. This is a few the many functions that make Linux a good choice for business.
I am a certified RHCT