A resistor is a circuit element that has a specific fixed or variable resistance.
Classification of resistors
By the nature of the change in resistance
Variable resistors or potentiometers
Trimmers (adjustable resistors)
By conductive material
Carbon : Film (CFR) or bulk
By installation method
PCB mounting: Hole mounting (Through-hole) or surface mounting (planar components , SMD)
For microcircuits (integrated resistors) and micromodules (hybrid microcircuits)
Special types of resistors
Resistors whose resistance varies depending on certain factors:
Varistors (dependence by applied voltage)
Thermistors (resistance by temperature): Negative-dependent thermistors (NTC) or positive-dependent resistors (PTC)
Photoresistors (dependence by illumination)
Strain gauges (resistance by supplied force)
Magnetoresistors (dependence by magnitude of the magnetic field)
Memristors (the resistance is depends on the history of current that had previously flowed through the device, "memory" effect)
Special Constructions