The standard unit for resistance is called the ohm after the German physicist Georg Ohm. Its symbol is the capital Greek letter Omega in the International System of Units and is the letter “R” in the British system of measurement.
Resistance is opposition to current, where current is the flow of charge. Resistors are examples of electrical devices that provide resistance inside a circuit. The most common ones are made from carbon and are available in many different sizes where ohms are the unit of measurement. Typical units are in tens or hundreds of ohms, but others are very small, such as milliohms for thousandths. Larger sizes are kilohms for thousands and megohms for millions. The larger the resistor, the larger the resistance or amount of ohms it provides. This translates into decreasing current flow inside the circuit as the resistance increases.