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 microgram is a unit of mass (acceptable for use as weight on Earth) and is a submultiple of an SI base unit with the symbol μg.
1 microgram is equal to 0.000001 or 1/1000000 g (one millionth of a gram).
The symbol μg is avoided in medical practises / applications because there is a chance the 'μ' could be misread as an 'm'; resulting in mg being interpreted rather than μg - which could lead to a 1000x overdose.