L means length in mathematics, and length is a measure of one-dimensional space and the distance from point to point. Usually, when measuring the side length of a line segment in two-dimensional space, the one with a large length value is called long, which is neither greater than its value nor wider than the side length.

The measurement of length is the most basic measurement, and the most commonly used tool is the scale. The international unit of length is meter (m), and commonly used units are kilometer (km), decimeter (dm), centimeter (cm), millimeter (mm), micron (micron) and nanometer (nm). When converting length units, small units are converted into large units by multiplication and large units are converted into small units by division.