An LCD, or Liquid Crystal Display, is a type of screen that is used in many computers, TVs, and cell phones. LCDs are very thin, but are actually composed of several layers. Those layers include two polarized panels, with a liquid crystal solution between them. Light is projected through the layer of liquid crystals and is colorized, which produces the visible image.
The liquid crystals do no emit light themselves, so LCDs require a backlight. That means that an LCD requires more power, and could potentially be more taxing on your phone’s battery. LCDs are thin and light, though, and generally inexpensive to produce.
Two types of LCDs are primarily found in cell phones: TFT (thin-film transistor) and IPS (in-plane-switching). TFT LCDs use the thin-film transistor technology to improve image quality, while IPS-LCDs improve on the viewing angles and power consumption of TFT LCDs.