Quasi-exact solutions of nonlinear differential equations

The concept of quasi-exact solutions of nonlinear differential equations is introduced. Quasi-exact solution expands the idea of exact solution for additional values of parameters of differential equation. These solutions are approximate ones of nonlinear differential equations but they are close to exact solutions. Quasi-exact solutions of the the Kuramoto–Sivashinsky, the Korteweg-de Vries–Burgers and the Kawahara equations are founded.