The pound 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 lb.
Not to be confused with a number of other definitions, the most common is international avoirdupois pound. The avoirdupois pound is defined as exactly 0.45359237 kilograms and is divided into 16 avoirdupois ounces.
One of the most common uses of the pound is in measuring the mass / weight of human beings or animals. When introduced, sports athletes such as boxers or wrestlers are described by their weight in pounds before any other characteristic as it helps people visualise how big / powerful they are.
The unit pounds originated from the Roman ‘libra’ (hence the abbreviated ‘lb’). The libra, which is Latin for scales or balance, was an ancient Roman unit used to measure mass and was equivalent to approximately 328.9 grams. The libra was originally split into 12 ounces (or unciae).
Random fact: Some cannons, such as the Smoothbore cannon, are based on the imperial pounds of circular solid iron balls of the diameters that fit the barrels. For example, a cannon that fires 12-pound ball is called a twelve-pounder.
The milligram is a unit of mass (acceptable for use as weight on Earth) and is a submultiple of an SI base unit with the symbol mg.
1 milligram is equal to 0.001 g or 1/1000 g (one thousandth of a gram).
There exists 2 submultiples between mg and g - namely the decigram and the centigram but these are not commonly used in everyday life. The milligram is commonly used when expressing parts of a gram; especially in medicine applications.
A mosquito weighs about 2.5 mg, as does a grain of sand.