The electric current is a flow of electric charge (a phenomenon) or the rate of flow of electric charge.
This flowing electric charge is typically carried by moving electrons, in a conductor such as wire; in an electrolyte, it is instead carried by ions, and, in a plasma, by both.
The SI unit for measuring the rate of flow of electric charge is the ampere. Electric current is measured using an ammeter.
In a HHO Cell the current is the electric charge that flows in the electrolyte between the electrolyzer plates.