A square number is a number that can be expressed as the product of an integer multiplied by itself. For example, the number 9 is a square number because it can be written as 3 × 3. Square numbers are always non-negative and include values like 0, 1, 4, 9, 16, and so on. Square numbers have various applications in mathematics, including geometry, where they can represent the area of a square with side lengths equal to the integer. The concept of square numbers is also foundational in algebra and number theory, influencing topics such as Pythagorean triples and quadratic equations.