Definition: 1. A force, such as friction, that operates opposite the direction of motion of a body and tends to prevent or slow down the body's motion. 2. A measure of the degree to which a substance impedes the flow of electric current induced by a voltage. Resistance is measured in ohms. Good conductors, such as copper, have low resistance. Good insulators, such as rubber, have high resistance. Resistance causes electrical energy to be dissipated as heat. 3. The capacity of an organism, tissue, or cell to withstand the effects of a harmful physical or environmental agent, such as a microorganism or pollutant.
Source: The American Heritage Science Dictionary. Boston: Houghton Mifflin, 2005. Credo Reference. Web. 17 August 2012.