Ubuntu is a Linux distribution. It is based on Debian. It is very popular as a desktop OS and as a Server OS. Ubuntu was originally geard towards providing a great, usable desktop experience for regular people. They wanted to bring Linux to the masses and make it more accessible. There was also a big focus on making things as free and open as possible. They did suceed at creating a very usable desktop system and even at getting Linux out to a wider userbase. Ubuntu provides a great usable desktop right out of the box with office software included by default. Tons of other software is available for easy install using the software center. They have also gone beyond the desktop. They now target servers, cloud systems, and IoT. All of these things are really easy to have up and running really quickly.