What device is used to display video images or data on a flat surface?

The device used to display video images or data on a flat surface is a Liquid Crystal Display (LCD). LCDs are widely used in various applications, including computer monitors, televisions, and digital signage. They function by using liquid crystals sandwiched between layers of glass or plastic, which allow light to pass through in a controlled manner, creating clear images.

LCD technology is favored for its ability to produce high-quality visuals with excellent color accuracy and brightness while consuming less power compared to traditional cathode-ray tube (CRT) displays. This makes them a popular choice for both professional and personal settings.

In the context of the question, while other options like smartboards and projectors do display video images, they serve different primary purposes or contexts. A smartboard functions interactively as a touchscreen interface for presentations and meetings, and a projector is typically used to project images onto a larger surface rather than being a standalone display device. Additionally, a monitor, while also a display device, is generally more associated with direct computer use rather than as a flat surface display method in the same context as LCDs.