Cathode
A cathode is a material that is giving up electrons because it has a higher electrochemical potential than a material that is connected to it by a conducting path. The path can be water, salt water, or even air if the voltage is high enough.
Most of us have seen an electron tube in operation at some point in our lives, even if it is in a museum. The glowing red part of the tube is the cathode. The plate or grid adjacent to the cathode is the anode. In an electron tube the temperature of the cathode is raised to increase the flow of electrons out of the cathode. In the case of a electron tube the space within the tube is as close to a vacuum as possible to increase the lifetime of the cathode. The currents in typical electron tubes range from milliamps to amps. Some electron tubes used for special purposes such as electro-dynamic shakers used to perform vibration tests on full scale hardware may have currents has high as hundreds of amps.
In the case of the electron tube the electrons drift from the cathode to the anode. The cathode is often referred to as the emitter and the anode is referred to as the collector. These terms are much easier to understand, since the are not Greek.
The voltages in electron tubes are much higher than those found in electrolytic corrosion which is why they can use air as a conductor. In the case of electrolytic corrosion, the voltages involved are so low that no significant current will flow across an air gap. This is why the rate of electrolytic corrosion can be almost zero in very dry conditions.