Fifth-order Korteweg–De Vries equation
A fifth-order Korteweg–De Vries (KdV) equation is a nonlinear partial differential equation in 1+1 dimensions related to the Korteweg–De Vries equation. Fifth order KdV equations may be used to model dispersive phenomena such as plasma waves when the third-order contributions are small.
Source: Wikipedia — Fifth-order Korteweg–De Vries equation (CC BY-SA 4.0)