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It is still used in the US despite its links to the much-outdated imperial system of units.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 board foot is a unit of volume derived from the imperial system of units with the symbol FBM.
1 board foot is equal to the volume of an object one foot in length, one foot wide and one inch thick. It is therefore equal to 1/12 ft³.
The board foot is the unit used to measure rough or planed lumber. For example 2 x 4 timber when planed actually only measures 1.5 in x 3.5 in. This takes into account the wastage when planing. The board feet measurement in this case would represent the wholesale amount. Where the loss in board feet (and planing) only applies to width and thickness, the actual length is used - as there is no loss when cutting lengths.