A two-terminal or one-port is an electronic component or circuit with two terminals. Such a two-terminal can be passive and frequency-independent like an ohmic resistor, passive and frequency-dependent like an inductor or capacitor, and also active
and frequency-dependent or frequency-independent. The resistance of a two-terminal can be linear or nonlinear as in the voltage-dependent varistor
, temperature-dependent asin hot conductors
or PTC thermistors
, frequency-dependentas in capacitors and coils, or brightness-dependent as in the photoresistor or photodiode
, or depend on other physical quantities.admittance can be represented in locus curves.