PTC is a positive temperature coefficient thermistor and NTC is a negative temperature coefficient thermistor.
PTC thermistors are used in circuit control and sensors, electric heating appliances and automobiles, compared with nickel, chromium wire or far infrared heating components, PTC thermistors mainly have the special functions of constant temperature, temperature regulation, automatic temperature control, non-combustion, safety and reliability, power saving, long life, simple structure, and wide voltage range.
NTC stands for negative temperature coefficient, and thermistors are divided into positive temperature coefficient and negative temperature coefficient thermistors. The symbol for a thermistor is a slash over the negative sign of the resistor. (Here can not upload the picture, the expression may be a little unclear)