A momentary electric discharge between two differently charged objects. Sparks
cross the air-gap between the objects along a narrow channel, which is visible
as a light flash.
Small painful spark discharges can occur when a person who is well insulated
from the ground through wearing shoes with plastic soles touches an object that
is electrically connected to the ground. If the electric currents are very small
(microshocks of less than 1mA) they are usually not
perceived.
A lightning discharge can be considered a large-scale spark discharge.
