Somewhere it is called fault current. It is seen in the circuit, sometimes when we switch off the line then we got shocked while touching it. this is due to the residual current. Also we can realize that the wire is a little bit heated when we make voltage suddenly to zero.
The main reason behind is the charge carriers ie; electrons. When the electrons are steadliy drifting in conductor wire it acquires current in the opposite of the motion of electrons. When the potential is reduced to zero instantaneously the voltage across the circuit becomes zero. In common sense there is no flow of electrons, but the drifting electrons have momentum because it has its own mass and velocity. At a instant time if it find ground or low potential it will recently discharge or earthen. If it don't get the way to flow the electrons having some momentum will collide with atoms in conductor and change their kinetic energy to heat energy. As we feel the wires hotter when we suddenly switch off.
It has also reverse process, when the wire is heated at zero voltage the free electrons in the conductor gain energy and start to flow on their favourable way, which is also called fault current.
These type of effect could cause harmful disaster in the area of use so safety measures are also used to control these problems in electronics and electrical mercenaries. Residual current circuit breaker, sensors etc are used to defeat these problems.
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