An op-amp stands for OPerational AMPlifier. It can converts the plus-or-minus 30 millivolts from your microphone into an output of plus-or-minus 2 to 3 volts. the LM741 is intended to be a bare-bones pre-amplifier, which increase the voltage from a very small input signal but cannot deliver significant power. A pre-amplifier is often referred as a preamp.