Every nonnegative real number has a unique nonnegative square root, called the "principal square root", which is denoted by formula_1 where the symbol formula_2 is called the "radical sign" or "radix". For example, the principal square root of 9 is 3, which is denoted by formula_3 because and 3 is nonnegative. The term (or number) whose square root is being considered is known as the "radicand". The radicand is the number or expression underneath the radical sign, in this case 9.