Avoirdupois is a system of measuring weight based on the fact that sixteen ounces are in a pound. The metric system is based on grams, and the avoirdupois system is based on pounds. - That's freedom units they're talking about.

And from the Avoirdupois System Wikipedia page - In 1959, by international agreement, the definitions of the pound and ounce became standardized in countries which use the pound as a unit of mass. The International Avoirdupois Pound was then created. It is the everyday system of weights used in the United States. It is still used, in varying degrees, in everyday life in the United Kingdom, Canada, New Zealand, Australia, and some other former British colonies, despite their official adoption of the metric system.