Thermistors have a negative temperature coefficient (TK) and are therefore also called NTC thermistors (NTC = Negative Temperature Coefficient).
They consist of mixtures of ceramic materials which determine their properties depending on the composition. Resistance values of 10Ω ... 1MΩ and operating temperatures of -50°C...350°C are possible.
If current flows through the thermistor or if the ambient temperature increases, the resistance decreases.
This behaviour can be used, for example, for temperature sensing, overcurrent limiting, inrush current limiting and heating purposes.