Plasma is superheated, compressed air that ionizes to form a conductive gas. This gas conducts electricity from the torch of the plasma cutter to the work piece, through a electrode and copper nozzle on the machine. The nozzle constricts the high velocity gas, causing a tornado effect, and the arc melts and blows away the metal.
Compared to oxyacetylene, which works by burning through the metal, plasma can cut through nonferrous materials, has a lower skill level and offers faster travel speeds. However, plasma cutters are more expensive that oxyacetylene units and require access to electrical power and compressed air, making them less convenient in some circumstances.