The expression "ax² + bx + c" represents a quadratic equation, where "a," "b," and "c" are constants, and "x" is the variable. The term "ax²" indicates that the equation is quadratic because it includes "x" raised to the second power. The graph of this equation is a parabola, which can open either upward or downward depending on the value of "a." In this equation, "a" cannot be zero, as that would make it a linear equation instead of quadratic. The values of "b" and "c" affect the position and shape of the parabola. Quadratic equations are commonly used in various fields, including physics, engineering, and finance.