Which of the following best describes a capacitor?

A capacitor is best described as an electrical component that stores electric charge. It consists of two conductive plates separated by an insulating material known as a dielectric. When voltage is applied across the plates, an electric field develops, allowing the capacitor to accumulate charge. This stored energy can then be released when needed in a circuit. Capacitors are commonly used in various applications, including energy storage, filtering noise in power supply lines, and in timing circuits.

The other options do not accurately describe the function of a capacitor. For instance, a device that measures voltage pertains to instruments like voltmeters, while a type of electrical conductor refers to materials that can conduct electricity, such as copper and aluminum. A mechanical device for motion control does not involve electrical energy storage, as it focuses on mechanical systems rather than electrical components. Thus, the definition provided in the correct answer captures the primary function of capacitors in electronic circuits clearly and succinctly.