A teleprompter, or autocue, is a display device that prompts the person speaking with an electronic visual text of a speech or script. Using a teleprompter is similar to using cue cards. The screen is in front of, and usually below, the lens of a professional video camera, and the words on the screen are reflected to the eyes of the presenter using a sheet of clear glass or a specially prepared beam splitter. Light from the performer passes through the front side of the glass into the lens, while a shroud surrounding the lens and the back side of the glass prevents unwanted light from entering the lens.
Source: Wikipedia