In practical applications, the capacitors and inductors used in electric circuits are not ideal components i.e. they do not only contain capacitance or inductance. However, they can be modeled as ideal capacitors and inductors in series with a resistance. This resistance is defined as the equivalent series resistance (ESR) and is sometimes referred to as a parasitic resistance due to its undesirable nature and side effects. These resistances contribute to power losses, cause undesirable phase shifts and may cause a reduction in the expected circuit current.