Current

Current is the usual measure of the flow of electricity in a conductor. The standardized symbol is I (capital letter I, best written with serifs) and the common unit is ampere or amp, abbreviated A (or mA, µA, etc). Today we know that in metallic conductors it electrons that flow, and electrons are assigned has having negative charge; however the early experimenters standardized the definition of current before this was known, so that conventional current, as represented directionally in circuits, is in the opposite direction to the actual movement of electrons.

In charged gasses, in fluid solutions, and with particle beams, current can comprise the movement of ions of either charge.