The fundamental quantity in electronics is charge and at its basic level is due to the charge properties of the fundamental particles of matter. For all intensive purposes it is the electron (or lack of electrons) that matter. The role of the proton charge is negligible.
The aggregate motion of charges is called current I
where dq is the amount of positive charge crossing a specified surface in a time dt. Be aware that the charges in motion are actually negative electrons. Thus the electrons move in the opposite direction to the current flow.
The SI unit for current is the ampere (A). For most electronic circuits the ampere is a rather large unit so the mA unit is more common.