F(t, y, dy/dt,....,dny/dtn) = 0;
this is an nth order ordinary differential equation. The order of a differential equation is the difference between its highest and lowest orders within the equation (with y being a zeroth order derivative). Consider
dy/dt + y = 0; this is a first order differential equation.
d2y/dt2 + dy/dt + y = 0; this is a second order.
for Example 1:
for Example 2:
for compartmental kinetics example