Equation whose graph does not form a straight line (linear) is called a Nonlinear Equation
More About Nonlinear Equations
In a nonlinear equation, the variables are either of degree greater than 1 or less than 1, but never 1.
Example of Nonlinear Equations
4x2 + 2y - 1 = 0 and x3 + 2x2 - 4xy - 1 = 0 are the examples of nonlinear equations.
is a nonlinear equation.