Natural user interface, or NUI, is the common parlance used by designers and developers of computer interfaces to refer to a user interface that is effectively invisible, or becomes invisible with successive learned interactions, to its users. The word natural is used because most computer interfaces use artificial control devices whose operation has to be learned. A NUI relies on a user being able to quickly transition from novice to expert. While the interface requires learning, that learning is eased through design which gives the user the feeling that they are instantly and continuously successful. This can be aided by technology which allows users to carry out relatively natural motions, movements or gestures that they quickly discover control the computer application or manipulate the on-screen content. A common misunderstanding of the "Natural User Interface" is that it is somehow mimicry of nature or that some inputs to a computer are somehow more 'natural' than others. In truth, the goal is to make the user feel like a natural.
Xbox Kinect
Xbox Kinect is a product from Xbox that uses spatial gestures for interaction instead of a game controller. According to Microsoft's page, Kinect is designed for a "a revolutionary new way to play: no controller required."