Width or breadth usually refers to a shorter dimension when the length is the longest one. Length is a measure of distance. In the International System of Quantities, length is a quantity with dimension distance. In most measurement systems, a base unit for length is chosen, from which all other units are derived. The base unit for length is the meter in the International System of Units (SI) system. Various terms for the length of a fixed object are used, including height, which is the vertical length or vertical extent, and width, breadth, or depth.