A perfect square number, also called square number, is the number that you get when you multiply some counting number by itself.
For example, 25 is a perfect square number because this is the number that you get when we multiply 5, a counting number, by itself.
Simply put, since 5 × 5 = 25, then 25 is a square number.
You can also think of a square number as a counting number that can be shown as an array in the shape of a square.
Notice how we can make an array in the shape of a square with 9 and 16. Therefore, 9 and 16 are perfect square numbers.