Electrical resistance (R) is the extent to which an electrical conductor hinders the flow of a current. Resistance is the ratio of the potential difference across an electrical component to the current passing through it. It is measured in ohms and is represented by the symbol R. In general, the resistance of a metallic conductor increases with temperature, whereas the resistance of a semiconductor decreases with temperature. In an alternating current, resistance is the real part of the impedance.
Resistance is characteristic of the material of which the conductor is made (the resistance presented by a unit cube of a material being called its resistivity) and of the physical dimensions of the conductor, increasing as the conductor becomes longer and/or thinner. Its accurate measurement is possible using a Wheatstone bridge.
Compare with conductance.