As seen above, an ordinary differential equation is one involving x, y, y', y'', and so on. Now add the idea that the order of the highest derivative is n. Thus, if a differential equation of order n has the form F(x, y', y'', …y⁽ⁿ⁾) = 0, then it is called an implicit differential equation. If it is of the form F(x, y', y'', … y^{(n - 1)}) = y⁽ⁿ⁾, it is called an explicit differential equation.