The square of a number is the number multiplied by itself.

5² = 5 * 5 = 25

In computer applications, squaring and other raising to a power is usually indicated by a ^ symbol.

5^2 = 5 * 5 = 25

The square root of a number is a number such that if it were squared it would return the original number. Technically, all positive real numbers have two square roots, a positive one and a negative one.

sqrt(25) = +5 and -5

However, in most applications, the negative root is ignored. In statistics, the square root of 25 is 5. Also remember that negative numbers do not have square roots (in the real number system).

sqrt(-25) is undefined or nonexistent or NaN (not a number)

The square root of 25 can also be written 25^1/2. Other roots generalize from that notation. The cube root of 25 is 25^1/3, and so on.