What is the difference between MIC and LINE level?

Level refers to the relative strength of the signal and is measured in decibels. LINE level sources are much-amplified signals over MIC (microphone) level signals. LINE level is normally -10 dBV for consumer gear and +4 dBu for pro gear while MIC levels are normally -60 dBu for dynamic microphones and -35 dBu for condenser microphones.