What is a perfect square number?

A perfect square number is a number that you get from taking

a positive or negative integer and multiplying it by itself.

A perfect square is a number that can be expressed as the product of two equal integers, like 9 which is 3x3, or 16 = 4x4, or 25 = 5x5, 49 = 7x7, etc. Number 6, for instance is not a perfect square because it cannot be expressed as the product of two equal integers : It's 2x3.