What is the resistance of a conductor?

Resistance is the opposition to the flow of electrons (i.e. electrical current) in a conducting material such as a metal wire or a pair of contacts in a switch. Every substance has a certain amount of resistance. Resistance is measured in ohms. If one volt can push 1 amp of current through a substance, it has a resistance of 1 ohm. Some materials, like copper and aluminum have fairly low resistance, and are therefore used as electrical conductors (wires).

Another answer

Conductor resistance means a material's opposition to the flow of current that a conductor has. Ideally, in a wire, this should be nothing, i.e. 0 ohms, but in reality all conductors have a certain amount of resistance. For example, 1000 feet of 14 AWG (the common wire size used for 15 amp branch circuits in residential wiring in North America) has about 2.5 ohms of resistance.

Further answers

Think of a conductor as a resistor/resistance of a certain very low value in series with whatever load it is feeding. Current flowing through the conductor(s) will result in a voltage drop and power loss, manifested as heating of the conductors. The "line loss" formula is one variation of the power formula and is P = I2 x R, which can be used for calculating the power loss in the conductors. Remember that any power line to a 120 volt device has 2 lengths of conductor going to it (hot and neutral return). Therefore the total conductor length is the length of the power cord or electrical cable times 2.

To calculate the voltage drop across the conductor resistance for a given current, you have to determine the conductor's resistance and use Ohm's law.

Calculating the resistance of a length of conductor can be done using tables readily available in textbooks or via a websearch, assuming copper conductors at 20 degrees Celcius. You need to know the size of the conductor (AWG size, for American wire gauge) and the length of the conductor.