The unit of electrical resistance is the ohm, represented by the symbol "Ω" (the Greek letter omega). It is named after Georg Simon Ohm, a German physicist who formulated Ohm's Law, which describes the relationship between voltage, current, and resistance in an electrical circuit.
One ohm is defined as the amount of resistance that restricts the flow of one ampere of current when one volt of potential difference is applied across it. In other words, if a voltage of one volt is applied across a resistor, and it allows one ampere of current to flow through it, then the resistance of that resistor is one ohm.
Mathematically, Ohm's Law is represented as:
Resistance (R) = Voltage (V) / Current (I)
So, if you know the voltage and current in a circuit, you can calculate the resistance, and vice versa.