Definitions for "Internal Resistance"
Resistance to electrical current created by reactance and ohmic resistance.
is just resistance. The redundant "internal" is often added when one is referring to something like a battery or an instrument.          symbol for joule, the SI unit of energy.
The quotient of the change of voltage of a cell or battery to the corresponding change of currentunder specified conditions. Alternating current(AC) and direct current(DC) measurment methods lead to very different values. The AC internal resistance is usually measured at 1000 Hz.