Generally speaking, both NTC and PTC belong to thermistor and which act as protecting the circuits.  As for their differences,

Difference 1:

NTC: Negative temperature coefficient thermistor, the higher the temperature, the lower the resistance.

PTC: Positive temperature coefficient thermistor, the higher the temperature, the higher the resistance.

Difference 2:

NTC handles the abnormality so that the circuit can be conducted normally, which is mainly used for temperature compensation, overcurrent protection, overheat protection, self-controlled heating, motor starting, color TV degaussing, etc.

While PTC recognizes the abnormality and cuts off the circuit, which is also mainly used for temperature compensation, overcurrent protection, overheat protection, self-controlled heating, motor starting, and color TV degaussing.