Electrical conduction is the movement of electrically charged particles through a transmission medium.
The movement can form an electric current in response to an electric field.
The underlying mechanism for this movement depends on the material.
Conduction in metals and resistors is well described by Ohm's Law, which states that the current is proportional to the applied electric field.
Metals are good conductors because they have unfilled space in the valence energy band.
Another medium, a "perfect vacuum," contains no charged particles; vacuums normally behave as very good insulators.
However, metal electrode surfaces can cause a region of the vacuum to become conductive by injecting free electrons or ions through either field emission or thermionic emission.