The efficiency of your brewing setup covers mash efficiency, boil off, deadspace during the boil and transfer and trub losses (the gunk left after the boil). Each of these will reduce your original gravity going into the fermenter. The number that captures all of these losses is called the Brewhouse efficiency. Brewhouse efficiency is typically about 72% for most home brewing size systems. Mash efficiency is a measure of the resulting original gravity against the expected original gravity.
