We live in a real world, surrounded by real people & objects and interact with them in a real space; however most of our digital data and information is restricted to a set of metaphors such as keyboard, mouse and screen. We have relied majorly on screen based text and graphics to interact with computer, specifically digital data or information for more than 3 decades. Consider it wall mounted screen, hand held device, head mounted displays etc.
Interfaces are not designed to immerse into spaces and objects, instead it forces people to interact with screen-based metaphors. We as human beings have a great ability to perform gestures, speech, remember interactions with natural objects; however computers do not use these mediums. They ask users to sit on a chair, play with keyboard, learn to use mouse, drop downs, software to know even a tiny set of information.
Here comes tangible user interfaces (TUI), where digital information is presented through interacting with physical metaphor. Physical objects play a central role as physical representations and control of digital information (augmenting physical and virtual realities). TUI thinks beyond desktop metaphor of mouse, keyboard, icon, drop-down, files, folders etc. and embeds information in real world.