1. The document discusses differential equations of higher order, which are equations where the derivatives are functions of higher algebraic order.
2. It provides examples of functions that are of higher order, and explains that a differential equation is of higher order if the functions P(x,y) and Q(x,y) are of higher algebraic order.
3. Methods for solving higher order differential equations are presented, including reducing them to an equivalent ordinary differential equation using appropriate substitutions, and then solving using standard integration techniques.