The peck is a unit of volume in the US customary unit system. It uses the symbol pk.
1 US peck is equal to 1/4 of a US bushel. This is also equal to 2 US dry gallons, 8 US dry quarts or 16 US dry pints. In SI / metric, this equates to 8.809768 L.
Although the imperial peck is almost obsolete, it survives in some places in the USA - where some products (namely apples) are still sold by the peck.
It appears in the old English nursery rhyme; 'Peter Piper' where he 'picked a peck of pickled peppers'.
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).