At constant / DC current, the current between two poles flows always in the same direction. The technical current flow moves from the higher potential point to the lower potential point. In case of AC current, the direction of current flow varies in time. For example in a 50 Hz network, the direction changes fifty times per second.
The AC current is mostly used for transporting electricity to consumers and for AC motors. Most of the electronic devices which are used today use DC current, e.g. laptops and mobile phones.
AC: power, reactive power, active power, apparent power,
DC: advantages, safety, limits,