Electrical resistance is somewhat like the electrical equivalent of friction in the mechanical world – it is the degree to which a material opposes, or resists, the passage of an electrical current. Good conductors have low resistance, insulators have high resistance. Electrical energy lost through resistance is converted into heat.
Resistance is measured in 'ohms', and under most conditions the resistance of an object is a constant, so it does not depend on the amount of the voltage or the amount of current passing through it. The relationships between current, voltage, and resistance are calculated using Ohm's Law.