The instrument that measures temperature is called a thermometer. Thermometers come in various types, including mercury, digital, and infrared, each serving different purposes. Mercury thermometers, which use liquid mercury to indicate temperature changes, are often used in scientific laboratories. Digital thermometers, commonly utilized in homes and medical settings, provide quick and accurate readings and are often employed for body temperature measurements. Infrared thermometers are used for non-contact temperature readings, making them suitable for applications like cooking and industrial measurements. Overall, thermometers are essential tools across various fields, including health care, meteorology, and research.