# What are squares of numbers?

A square is when a number is muliplied by itself. For example, 9 is the square of 3. 16 is the square of 4, and 25 the square of 5.

### Which numbers are not square number's?

In the complex field, every number is a square so there are no numbers that are not squares. If the domain is reduced to that of real numbers, any negative number is not a square. However, the term "square numbers" (not number's!) is often used to refer to perfect square numbers. These are numbers that are squares of integers. Therefore the squares of fractions or irrational numbers are non-squares.