Linux or GNU/Linux is a free and open source software Unix-like operating system for computers. An operating system is a collection of the basic instructions that manage the electronic parts of the computer allowing running application programs.
Linux is Free and open source software (FOSS). Free and open source software (FOSS) means that everyone has the freedom to use it, see how it works, change it or share it. There is a lot of software for Linux and—like Linux itself—a lot of the software for Linux is free software. This means that it doesn't put any license restrictions on users.
This is one reason why many people like to use Linux. The defining component of Linux is the Linux kernel. Because of its openness and security, Linux is also the prominent operating system in professional astronomical observatories. While the amateur astronomer market is still dominiated by Windows, Linux is making headways with INDI and Ekos. Ikarus Observatory equipment are connected to Raspberry PI 2, a credit-card size single board computer, running Debian Linux Jessie version with the latest stack of INDI server, tools, and drivers. The client machine is running Kubuntu 15.10 with KDE Plasma 5.4.