A fluid ounce is a measurement of liquid. There are twenty fluid ounces in a British pint, and sixteen in an American pint.
fluid ounce in British English
noun
a unit of capacity equal to the volume of one avoirdupois ounce of distilled water at 62°F: there are twenty fluid ounces in an Imperial pint and sixteen in a US pint
fluid ounce in American English
noun
a unit of liquid measure, equal to 1⁄4 gill or 1⁄16 pint or 8 fluid drams (29.5734 milliliters): the British and Canadian imperial fluid ounce equals 1⁄20 of an imperial pint or 28.4122 milliliters