A thermometer is a device used to measure temperature. It can tell us how hot or cold something is, whether it's the weather outside or the temperature of our body. There are different types of thermometers, including digital ones that show the temperature on a screen and traditional glass ones filled with liquid like mercury or alcohol. Thermometers are important tools in many fields, such as medicine and cooking. For example, a medical thermometer helps doctors check if someone has a fever, while a cooking thermometer ensures that food is cooked to the right temperature for safety and taste.