mastering (a _really_ rough definition) is editing of a 2 track after mixdown.. things such as adjusting overall eq, fixing levels, etc are done... it's NOT something very many home recordists are capable of doing (well) and it is usually considered sonic suicide to master your own mixes... the general consensus is that homerecordists should just concentrate on geting the best possible mix through appropriate tracking techniques (choosing and utilizing mics, recorders, preamps, etc) as well as appropriate mixing techniques (setting levels, effects, not-mixing-in-the-same-day-as-tracking, etc) and then leave the mastering to a professional