An example might be a resistor-capacitor filter in electronics. The charge on the capacitor will be the integral of the current you pour into it (and the voltage across it proportional to the charge). However if the capacitor is in parallel with a resistor, it will discharge ("leak") through that resistor. Thus it's equation of motion will be
$$ I = C{dV\over dt} + V/R $$
which you can re-arrange to get the ODE shown on the Wikipedia.