From Longman Business Dictionary
avoirdupoisav·oir·du·pois /ˌævədəˈpɔɪz, ˌævwɑːdjuːˈpwɑːˌævərdəˈpɔɪz/ noun [uncountableU] a system of weighing things used in the UK and US, based on the standard measures of the OUNCE, POUND, and TON, which is being replaced in the UK by the METRIC SYSTEMThere are 16 ounces to one avoirdupois pound.