A thermistor (or thermal resistor) is defined as a type of resistor whose electrical resistance varies with changes in temperature. Although all resistors’ resistance will fluctuate slightly with temperature, a thermistor is particularly sensitive to temperature changes. Thermistors act as a passive component in a circuit. They are an accurate, cheap, and robust way to measure temperature. While they do not work well in extremely hot or cold temperatures, they are the sensor of choice for many different applications. They are ideal when a precise temperature reading is required.
E.g.: Toasters, coffee makers, refrigerators, freezers, hair dryers, etc. all rely on thermistors for proper temperature control.