The length determines the distance between two points, or in other words, it is the amount of space between two points. For example, the distance between my house and school, or the distance from one end of the table to the other.
The principal unit for measuring length is the meter.
Multiples are the units of measurements which are bigger than the meter. They are the decameter, hectometer, and the kilometer. There are more, but right now we are only going to look at these.
Submultiples are the units of measurement which are smaller than the meter. They are the decimeter, the centimeter, and the millimeter.