Direct current
From Computer History Wiki
Direct current (often abbreviated as DC) refers to the current (and thus voltage) pattern used in one of the two main methods of carrying power (the other being so-called alternating current, or AC).
In DC, there is a constant flow of electrons in one direction, at an unchanging rate. (Sometimes an AC signal will be superimposed on a voltage offset, producing a unidirectional flow of electrons, but this is usually only for signal processing purposes.)
AC is preferred over DC for power transmission; DC is preferred for digital logic circuitry.
