Type of equations, separated by degree:
Equation of first degree, linear equation:
kx + d = 0
Equation of second degree, quadratic equation:
ax2 + bx + c = 0
Equation of 3rd degree, cubic equation:
ax3 + bx2 + cx + d = 0
When applied it gives a scheme to correctly calculate a figure in a coordinate system.
As correctly pointed out by BrianShader, the list goes on forever. After the cubic equation there is the quartic equation, then there comes the quintic...