In mathematics, a quadratic equation is a polynomial equation of the second degree. The general form is
ax^2 + bx + c = 0,
where a ≠ 0. (For a = 0, the equation becomes a linear equation.)
The letters a, b, and c are called coefficients: the quadratic coefficient a is the coefficient of x2, the linear coefficient b is the coefficient of x, and c is the constant coefficient, also called the free term or constant term.
Quadratic equations are called quadratic because quadratus is Latin for "square"; in the leading term the variable is squared.
Reference:
http://en.wikipedia.org/wiki/Quadratic_equation
