The acre-foot is a unit of volume in the US customary unit system with the symbol ac⋅ft.
It represents the volume contained in a box measuring 660 feet long, 66 feet wide and 1 foot deep. This can be thought of a box the size of an acre but 1 foot deep.
It is approximately the same volume as an 8 lane swimming pool; 25 metres in length, 3 metres deep and 16 metres wide (assuming lanes are 2 metres wide).
It is still used in the US despite its links to the much-outdated imperial system of units. For example a "rule of thumb" is that an average suburban family's annual water usage should be around 1 acre-foot. This is equal to just under 3.4 m³ daily.
The US fluid ounce is a unit of volume in the US customary unit system with the symbol fl oz.
Primarily used for measuring the volume or capacity of liquids, 1 US fluid ounce is equal to 29.57353 ml. It is also equal to 1.040843 imperial fluid ounces.
1 US fluid ounce is equal to 1/16 imperial pint, 1/32 imperial quart and 1/128 imperial gallon.
The fluid ounce was originally defined by the volume taken up by one ounce of a substance. Of course this would be different depending on the density of that substance; for example England used wine whereas Scotland used water to establish this measure.
The US fluid ounce is derived from the US gallon; which was originally based on the English wine gallon (231 cubic inches).