There are flat screens, displays for laptops, projectors, little PDA screens, etc. etc. Flat Panel screens LCD displays - used for laptops and other small flat displays such as a digital watch. These monitors can display colors, but on smaller displays like a watch the color eats up the battery life too quickly. LCD stands for liquid crystal display and that is how the data is displayed. Liquid crystals between two sheets of glass.
Electricity is used to energize the crystals so they allow more or less light through.
Gas Plasma screens - These are usually larger screens, they use gas instead of the liquid crystals, but the technology is similar. As the cost comes down look for HDTV's to be a televison set and a computer monitor. The quality of the output for your computer is dependent on the quality of your video card as it is of your monitor. A video card is enhancement card that usually plugs straight into one of the enhancement slots on the Motherboard. The monitor plugs directly into the video card.