A unit of resistance. (Pronounced Home, with a silent H.) It is the measure of the opposition offered to the flow of current in an electrical or electronic circuit. Resistance is usually the product of a resistor. The resistance offered by a column of Mercury 106.e centimeters in length and 1 square millimeter in cross-sectional area, at 32 degrees Fahrenheit or 0 degrees Celsius. One ohm is the resistance value through which one volt will maintain a current of one ampere.