A liquid-in-glass thermometer is a device used to measure temperature. It consists of a glass tube filled with a liquid, usually mercury or colored alcohol. As the temperature rises, the liquid expands and moves up the tube, indicating the temperature on a calibrated scale. These thermometers are commonly used in laboratories, homes, and weather stations. They provide accurate readings and are easy to read. However, mercury thermometers are being phased out in many places due to safety concerns, leading to a preference for alcohol-based alternatives.