The unit that measures electrical resistance is the ohm (symbol: Ω). Named after the German physicist Georg Simon Ohm, the ohm quantifies how strongly an object opposes the flow of electric current. Resistance plays a vital role in electrical circuits, determining how much current flows for a given voltage according to Ohm's Law, which states that voltage (V) equals current (I) times resistance (R) (V = IR). Understanding resistance helps engineers and electricians design and analyze circuits to ensure they operate safely and effectively in various applications.