The "difference of squares" is a mathematical concept that refers to the expression formed by subtracting one square number from another. It can be represented as a² - b², where a and b are any real numbers. This expression can be factored into the product of two binomials: (a + b)(a - b). This property is useful in algebra for simplifying expressions and solving equations. For example, if you have 9 - 4, you can recognize it as 3² - 2², which factors to (3 + 2)(3 - 2) = 5 × 1 = 5. Understanding this concept helps in various mathematical applications.