A thermocouple is a device used to measure temperature. It consists of two different types of metal wires joined at one end. When the joined end is heated or cooled, it produces a small voltage that can be measured. This voltage changes with temperature, allowing for accurate temperature readings. Thermocouples are widely used in various applications, including industrial processes, HVAC systems, and scientific research. They are popular because they are durable, can measure a wide range of temperatures, and respond quickly to changes. Common types of thermocouples include Type K, Type J, and Type T.