Linux, or more properly GNU/Linux, is a community-developed operating system and suite of programs. Released under the General Public License, it follows the rule of four freedoms: to run the program for any purpose, to study how the program works and change it so it does what you wish, to redistribute copies to your neighbors, and to distribute any modifications you have made to others. GNU/Linux is developed by hundreds of thousands of individuals, and is highly resistant to most Internet threats. And as you can see, it’s entirely free!
Ubuntu Linux is a specific distribution, maintained by a company named Canonical, that offers a packaging of GNU/Linux that is easy and accessible for novice users. It provides a full office suite, modern browsers, support for Flash and PDFs, and can support other peripherals such as scanners and cameras without hunting for drivers.
It cannot natively run Windows-based programs, so it is not suitable for PC Gaming, and Netflix has yet to support the platform. However, it also cannot run Windows malware and viruses, and is historically more stable than any other operating system. If you want a safe Internet environment for online banking, web surfing, and checking email, Ubuntu Linux could be right for you.
It can also be installed alongside your Windows or Mac operating system, so you don’t need a second computer.
(Trivia: Ubuntu is named after the Southern African philosophy of ‘humanity towards others’)