Gain

A microphone puts out a very small signal. Gain is the amplification applied to bring it up to a usable level. Set it too low and you have to raise the recording afterwards, which lifts the noise floor along with the voice. Set it too high and the loudest moments clip, and nothing in post repairs that. Aim for peaks around minus 12 to minus 6 dBFS. Dynamic microphones need far more gain than condensers, which is why a budget interface sounds thin and hissy behind an SM7B.