The basic unit of distance is the METER, which is a five letter word. The METER is a unit of length in the International System of Units (SI). It is equal to the length of the path travelled by light in a vacuum in 1/299, 792, 458 of a second. The METER was originally defined in 1799 as one ten-millionth of the distance from the equator to the North Pole. It is now defined as the distance that light travels in a vacuum in 1/299, 792, 458 of a second.