Parasitic impedance

Component designers will strive to minimise parasitic elements but are unable to eliminate them.

Discrete components will often have some parasitic values detailed on their datasheets to aid circuit designers in compensating for unwanted effects.

For wound components such as inductors and transformers, there is additionally the important effect of parasitic capacitance that exists between the individual turns of the windings.

For instance, the inter-winding capacitance mentioned above is really a distributed element along the whole length of the winding and not a capacitor in one particular place.

Designers sometimes take advantage of parasitic effects to achieve a desired function in a component, see for instance helical resonator or analog delay line.