The movement of electrons inside a conductor is called electric current.
When the electrons move along in the same direction, the current is said to be direct.
When the electrons oscillate back and force, the current is said to be alternating.
Direct electric currents take place when we connect a wire to both the terminals of a battery.
Alternating current (AC) is produced by generators, when a coil moves in the presence of a magnet, causing the electrons in the coil to move. (See generator)
The following two visuals illustrate the two different types of electric current.

The intensity of the electric current is due to the number of electrons that go through (or oscillate around) each section of the conductor. It is measured in amperes (the charge going through the section in coulombs divided by the time taken in seconds).