Lane Emden Equation is this ordinary differential equation.
The "ξ" is independence variable and means radius of a star. The "θ" is a function depend on ξ.
The value of θ equals 1 in the center of the star, and equals 0 in the surface.
The "n" is a parameter that characterizes the equation and called polytropic index.
Lane Emden Equation is very important for astrophysics.
If you want to know details of this, please see Wikipedia!