Ubuntu is a free operating system based on GNU/Linux. It is tailored for the mainstream desktop user and comes pre-installed with a variety of software for tasks such as office, multimedia, internet etc. It can be run directly from the CD without installation, be installed inside of windows -much like any other application- or be installed in its own dedicated partition.
Ubuntu also offers free access to thousands of free applications for almost every task imaginable.
EDIT: WOW I was downvoted to -5 within 1/2 a minute? Hotukdeals is surely infested with bots.