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 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.