fluid ounce

Short definition from Wiktionary

Noun

1. 1
   Any of various units of volume used for liquid measure, all approximately 1.73–1.83 cubic inches or 28.4–30 milliliters: A unit of volume equal to one sixteenth of a US pint or approximately 29.6 ml
2. 2
   Any of various units of volume used for liquid measure, all approximately 1.73–1.83 cubic inches or 28.4–30 milliliters: A unit of volume equal to one twentieth of an imperial pint or approximately 28.4 ml