The expression "b² - 4ac" is known as the discriminant in the context of quadratic equations, which are typically written in the form ax² + bx + c = 0. The discriminant helps determine the nature of the roots of the equation. If the discriminant is positive, there are two distinct real roots; if it is zero, there is exactly one real root; and if it is negative, the roots are complex or imaginary. In practical terms, the discriminant provides valuable information about the solutions of a quadratic equation without needing to solve it completely. This makes it a useful tool in various fields, including mathematics, physics, and engineering, where understanding the behavior of quadratic functions is essential.