The expression "a² - b²" represents the difference of squares, a fundamental algebraic identity. It can be factored into the product of two binomials: (a + b)(a - b). This means that the difference between the squares of two numbers can be expressed as the product of their sum and their difference. This identity is useful in various mathematical applications, including simplifying expressions and solving equations. It helps in factoring polynomials and can be applied in areas such as geometry and calculus, making it a valuable tool for students and professionals alike.