Resistance as a quantity is symbolized by the letter "R" in algebraic equations. It is measured in units called ohms, which are abbreviated as "Ω," the capitalized Greek letter omega. In electronics, resistance is the opposition, or friction, against electron flow, or current, through conductors in an electrical circuit.
Resistance measurements in equations are used to determine current and voltage, the force that motivates the flow of electrons. Georg Simon Ohm first discovered that voltage, symbolized by the letter "E," is equal to current, symbolized by the letter "I," multiplied by resistance. This is known as Ohm's law, which can be expressed with the equation E = I x R. When two out of three of the variables in the equation are known, algebra can be used to solve the third variable.