Linux is an operating system. Basically operating system is a software that manages computer hardware resource and provides interface to run other programs. You must have operating system installed on your computer like Windows, Mac, Linux or any other.
Operating System acts as a mediator between hardware and user software. Linux is very popular Unix like operating system. It was first released in 1994 with version 1.0. It is a multi-tasking and multi-user operating system.
Linux is open source version of Unix. Linux kernel code is publicly available. You can take Linux kernel code, modify it and create your own operating system.
Since Linux kernel is open source, many communities and companies made specific operating systems by using Linux kernel. These specific operating systems are known as distribution of Linux. Following are few popular Linux distributions: