What electrical parameter is controlled by a potentiometer?

A potentiometer is fundamentally a variable resistor. By turning a shaft or moving a slider, a wiper moves across a resistive strip. This physical movement directly changes the amount of electrical resistance between the wiper and the end terminals. While adjusting a potentiometer in a live circuit will indirectly cause changes to voltage and current (following Ohm's Law), the actual physical parameter built into and controlled by the component itself is resistance. It does not possess or control inductance, capacitance, or magnetic field strength.