Ohm's law defines the relationship between voltage, current, and resistance in electrical circuits. It states that if voltage is applied to a resistance, current will flow and power will be consumed. The law establishes that voltage is measured in volts, current in amps, and resistance in ohms. Using Ohm's law, electricians can calculate any two of these values if the third is known. Understanding Ohm's law is essential for designing and troubleshooting electrical and electronic circuits.