In general English usage, length (symbols: l, L) is but one particular
instance of distance ï¿½ an object's length is how long the object is ï¿½ but in the
physical sciences and engineering, the word length is in some contexts used
synonymously with "distance". Height is vertical distance; width (or breadth) is a lateral
distance; an object's width is less than its length.
No one speaks of "the length from here to Alpha Centauri", but rather of "the
distance from here to Alpha Centauri," but when one speaks of distance more
abstractly, one says "A kilometre or a mile, is a unit of length" or "...of
distance", and the two statements are synonymous. Likewise, a mountain might be a mile in height. Length is the metric of one
dimension of space. The metric of space itself is volume, or (length)3.
Length is commonly considered to be one of the fundamental units, meaning that
it cannot be defined in terms of other dimensions.