The kilogram is the base SI unit for mass (acceptable for use as weight on Earth). It uses the symbol kg.
It is the only SI base unit with the prefix as part of its name (kilo). The word is derived itself from the French 'kilogramme' which was itself built from the Greek 'χίλιοι' or 'khilioi' for 'a thousand' and the Latin 'gramma' for 'small weight'.
It is now used worldwide for weighing almost anything - and has quickly become commonly recognised and understood by the masses. It is sometimes shortened to 'kilo' which can cause confusion as the prefix is used across many other units.
In 1795 the kilogram was first used in English and was defined as the mass of one litre of water. This provided a simple definition but when used in practice it was difficult as trade and commerce often involved large items. Weighing a large object using large quantities of water was inconvenient and dangerous. As a result, an object made out of a single piece of metal was created equal to one kilogram. This platinum-iridium metal, called the International Prototype Kilogram, has been kept in Sèvres, France since 1889.
The ounce is a unit of mass (acceptable for use as weight on Earth) and is part of the imperial system of units. It has the symbol oz.
Not to be confused with a fluid ounce (fl oz; volume) or an ounce-force (force), the ounce is the smallest of the 3 denominations of weight used in the imperial system. There are 16 ounces in a pound and 14 pounds in a stone.
The strict name for this unit is the avoirdupois ounce and in SI / metric terms it is equivalent to approximately 28.3g.
Ounces are used to indicate the weight of fabrics in Asia, the UK and North America. For example, 16 oz denim. The number refers to weight of the fabric in ounces.
The ounce was no longer seen as a legal unit of measure after the year 2000 in the UK. However, it is still used informally and is also used as the measure for portion sizes in restaurants in the UK.