The electrical resistor of an electrical element is the opposition to a flowing of an electric current through that element. Using the flow analogy, electrical resistance is similar to friction. For water flowing through a pipe, a long narrow pipe provides more resistance to the flow than does a short fat pipe. The resistor (R) of a material depends on its length, cross-sectional area, and the resistivity, which depends on the material.

If we have a wire with length L and section S, its resistor R is:

with being a constant known as resistivity, which depends on the material of which the wire is made.

The standard units of measurement of the resistance R is Ohms (Ω) in

A conductor is a resistor of 1 ohm (1 Ω) when it allows a 1 ampere current to flow through it when the 1 voltage is applied to it.

1 Ω=

It is interesting to note that conductor wires used in electrical circuits have a very little resistor, although sometimes it is necessary a very low level of current to flow through a conductor or a part of the circuit. The resistance in that part must be very high in order to do this.

Objects with a little resistance are good conductors, while objects with a high level of resistance are bad conductors, normally named as insulators.

https://www.khanacademy.org/science/physics/electricity-and-magnetism/v/circuits--part-1 [EN] (open in new window)