Purpose of this Resistor in Circuit attached
R2 is often on opamp outouts .Like John D commented it provides some capacitive load isolation .It also isolates RF and is sometimes referred to as a "Stopper resistor".For termimation you assume that the opamp has zero output impedence so in your example the circuit has an output impedance of 33R .The resistor does not waste much output voltage and can allow for easy trouble free paralleling of opamps in order to get more current .Real loads have inductance and capacitance which can not always be ignored .You can get ringing if there is a highish Q .The series resistor reduces the Q and hence the ringing .I have heard the term "Damping resistor" used in the old days.