Electrical resistivity (also known as specific electrical resistance or volume resistivity) is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electrical charge.

Definition provided by wikipedia

Resistivity

Resistivity part 2

Resistivity is a result of couple things.

1.    The amount free electron the material have.  Metals tend to have a lot of free electron the move randomly in the wire; low resistivity.  Other materials such as wood and even water don't have a lot (if any); high resistivity.

2.    The rate of collisions in the wire. electrons move randomly in the wire, its a net motion that produces a current. As a matter of fact the electrons released from the potential will probable never reach the other end of the wire. The collisions in the wire slow down the flow.

3.     Temperature can seriously effect the resistivity.  Temperature is nothing more then particule motion, when particules move then the rate of collision will increase, which in turn increases the resistivity.