An electron is a subatomic particle usually found in orbit around an atomic nucleus. It is by definition said to have one unit of negative electrical charge.

Current is nothing more than electrons in motion. The ampere is the standard measure of current. How many moving electrons create an ampere? The short answer—without supplying a historical pedigree—is about six billion billion electrons, rushing by in the space of one second.

As a raw number of charges, going nowhere (perhaps stored, as a static charge, on a sweater just out of the dryer), six billion billion electrons make up a standard handful called a coulomb. Charges moving at the rate of one coulomb per second constitute one ampere of current. This may seem an immense dislocation in a length of, say, 12-gauge copper wire, but the truth is that loose, outer electrons do a lot of hopping from atom to atom, forming a confused cloud.

An applied voltage instantly sets up a pronounced drift within the otherwise aimless cloud. If you could observe and time the progress of any single electron—there are good theoretical and practical reasons why you cannot—you would clock its net advance at only an inch or less per second. (Of course, charges moving in a vacuum, as between an electron gun and a TV screen or in a particle accelerator, can indeed reach enormous speeds.).