Length
From AoPSWiki
In mathematics, length is the distance between an object's ends, or endpoints. It is the long dimension of an object.
Units of Length
Standard units are used to measure the length of an object.
In the International System of Units (SI), the basic unit of length is the meter (or metre), and is defined in terms of the speed of light. Other commonly used units, all derived from the meter, are the millimeter, centimeter, and kilometer.
In the Imperial System of Units, commonly used units of length are the inch, foot, yard, and mile.
