Why the electric current is known as the flow of free electrons.

Why we are not saying that the electric current is known as the flow of protons.

More precisely, the flow of electrons is an electric current. Protons do not flow in an electric circuit; they stay fixed in place because they’re much heavier than the electrons. However, protons can flow in a plasma. In that case, the flow of protons is also called an “electric current.”

By convention, the direction of flow of electric current is opposite the direction of electron flow. In a plasma, if protons are moving, the resulting current is in the same direction as proton flow.