What is the Ounce ?

Source: en.wikipedia.org

" The ounce is the name of several different units of mass, weight or volume and is derived almost unchanged from the uncia, an Ancient Roman unit of measurement.
The avoirdupois ounce (exactly 28.349523125 g) is 1⁄16 avoirdupois pound; this is the United States customary and British imperial ounce. It is primarily used in the United States to measure packaged foods and food portions, postal items, areal density of fabric and paper, boxing gloves, and so on, but is sometimes used also elsewhere in the Anglosphere. (...) "