A unit of length is a standard measurement used to quantify distance or size. Common units include the meter, centimeter, and kilometer in the metric system, while the inch, foot, and mile are used in the imperial system. These units help people communicate measurements clearly and consistently. Units of length can be converted from one system to another. For example, 1 meter is approximately equal to 39.37 inches. Understanding these units is essential in various fields, including science, engineering, and everyday activities like measuring furniture or distances traveled.