Body resistance
The voltage necessary for electrocution depends on the current through the body and the duration of the current. Ohms law states that the current drawn depends on the resistance of the body. The resistance of human skin varies from person to person and fluctuates between different times of day. The NIOSH states "Under dry conditions, the resistance offered by the human body may be as high as 100,000 ohms. Wet or broken skin may drop the bodys resistance to 1,000 ohms," adding that "high-voltage electrical energy quickly breaks down human skin, reducing the human bodys resistance to 500 ohms".The International Electrotechnical Commission gives the following values for the total body impedance of a hand to hand circuit for dry skin, large contact areas, 50 Hz AC currents (the columns contain the distribution of the impedance in the population percentile; for example at 100 V 50% of the population had an impedance of 1875Ω or less):

Skin
The voltage-current characteristic of human skin is non-linear and depends on many factors such as intensity, duration, history, and frequency of the electrical stimulus. Sweat gland activity, temperature, and individual variation also influence the voltage-current characteristic of skin. In addition to non-linearity, skin impedance exhibits asymmetric and time varying properties. These properties can be modeled with reasonable accuracy. Resistance measurements made at low voltage using a standard ohmmeter do not accurately represent the impedance of human skin over a significant range of conditions. For sinusoidal electrical stimulation less than 10 volts, the skin voltage-current characteristic is quasilinear.
Shortly thereafter, in 1892, the term was used in Science to refer generically to death or injury caused by electricity. Factors in lethality of electric shock
The lethality of an electric shock is dependent on several variables:

Current. The higher the current, the more likely it is lethal. Since current is proportional to voltage when resistance is fixed (ohms law), high voltage is an indirect risk for producing higher currents. Duration. The longer the duration, the more likely it is lethal—safety switches may limit time of current flow
Pathway. If current flows through the heart muscle, it is more likely to be lethal. High voltage (over about 600 volts). In addition to greater current flow, high voltage may cause dielectric breakdown at the skin, thus lowering skin resistance and allowing further increased current flow. Medical implants. Artificial cardiac pacemakers or implantable cardioverter-defibrillators (ICD) are sensitive to very small currents. Pre-existing medical condition. Age and sex.Other issues affecting lethality are frequency, which is an issue in causing cardiac arrest or muscular spasms. Very high frequency electric current causes tissue burning, but does not penetrate the body far enough to cause cardiac arrest (see electrosurgery). Also important is the pathway: if the current passes through the chest or head, there is an increased chance of death. From a main circuit or power distribution panel the damage is more likely to be internal, leading to cardiac arrest.