An ESR is the Equivalent Series Resistance of an electrical component (such as capacitors and inductors) arising from non-idealities always present in the manufacturing.

ESR is the "equivalent series resistance" of an electrical component (such as a capacitor or inductor) arising from non-idealities that are always present in the materials used in their construction.

An ESR is the Equivalent Series Resistance of an electrical component (such as capacitors and inductors) arising from non-idealities always present in the manufacturing.