Feedback

Feedback makes it possible for a user interface to exist, as it shows the person performing the act of input, that there is an outcome to their actions. Feedback exists to make user interfaces easier to stand and manipulate. It also exists to guide the user in their actions.
 * Feedback**, in terms of interactivity, is basically the input or action that a person performs with something, which results in some sort of an output. It can also be referred to as a process whereby some proportion of the output signal of a system is passed back to the input.

//Examples:// 1) A person typing on a computer keyboard is a good example because as the person types, letters appear on the screen of the computer, the person is giving the input and the computer screen is showing the output. 2) Another example is a person using an ipod because they give an input by using the clickwheel to select a song and the ipod responds by playing the selected song, in other words it is giving output. 3) A very simple example is of a person turning a door handle and pushing a door in order to open it, the door opening is the output. 4) A person that has not selected anything on the computer has pressed delete, however the computer does not know what to delete and therefore informs the user that there is an error with a sound of a beep.

Sources: "Feedback." Wikepedia. Retrieved January 16, 2008 from http://en.wikipedia.org/wiki/Feedback. "Feedback." The New Oxford American Dictionary, 2nd Edition.