Resistance is opposition to the flow of current and is measured in ohms (Ω). One ohm is defined as the amount of resistance that will allow one ampere of current to flow if one volt of voltage is applied. As resistance increases, current decreases as resistance and current are inversely proportional.
You would measure the amount of resistance at a certain point in a circuit with a(n):
ammeter 

voltmeter 

ohmmeter 

potentiometer 