Linux is an open source operating system created by Linus Torvalds. It has many flavors like Red Hat Enterprise Linux, Ubuntu, Debian, Fedora etc. Open source means that you can check the source code and study it. From laptops to mobile phones and cars to home appliances Linux is used everywhere.
The core part of Linux is the kernel. Kernel controls all major functions like memory, scheduling, hardware configuration etc. On top of it there is graphical server which provides Graphical User Interface. There there are lot of applications which can be installed and used.
Linux has multiple flavors. You can choose any flavor which suits you. As Linux is free and open source there is every kind of software available for you to use.