Ubuntu is free open-source software, that, along with its openness, provides a stable, secure, full-fledged platform, used and enjoyed by millions and millions of users across the world.
While, for users familiarized with Ubuntu, the open-source software and its "directions" are known and appreciated, for newcomers coming from the proprietary world, the openness is perceived as exciting yet "mysterious", in the sense of not being able to understand how an open community is built, sustained and constantly developed and enhanced.