The device used to measure temperature is called a thermometer. Thermometers can be found in various types, including digital and traditional mercury models, and are used to measure body temperature, environmental temperature, and other substances' temperatures. In clinical settings, digital thermometers are widely preferred for their speed and accuracy. Specific types of thermometers, like infrared thermometers, are also utilized for non-contact temperature readings. Overall, thermometers play a crucial role in medicine, meteorology, and many scientific fields, helping monitor and manage temperature-related conditions effectively.