For the case of more than one variable, see Conic section or Quadratic form.

In elementary algebra, a quadratic equation (from the Latin quadratus for "square") is any equation having the form

where represents an unknown, and , , and represent known numbers such that is not equal to . If , then the equation is linear, not quadratic. The numbers , , and are the coefficients of the equation, and may be distinguished by calling them, respectively, the quadratic coefficient, the linear coefficient and the constant or free term.