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.
The tonne is a unit of mass (acceptable for use as weight on Earth) and is a non-SI metric unit. It has the symbol t.
1 tonne is equal to 1000 kg. In the US it is called a metric ton (to avoid confusion with other similarly named units like the short ton, the long ton and the register ton. It is equal to approximately 2204.6 lbs.
Tonne is the correct spelling in England and France although ton is acceptable across the world. Before the establishment as an SI-derivative (or metrication), the ton (or imperial ton) was equal to 2240 avoirdupois pounds (or 20 hundredweight). This is only 16 kg different from the up to date (metric) tonne as we know it today.
A car weighs about a tonne.