Answer: unit
Jusitification:
An plain number does not inform the real meaning of the measure if you do not inform the unit of measurement.
Without the unit you cannot tell the real magnitude of objects or phenomena measured.
For example, suppose that some one asks how long is a boat and the answer is 20. What is it? 20 meters? 20 feet? 20 yards? You do not really know if it is a big boat or a small one until you inform the unit of measurement.
The same is true with any measurement. If you measure volumen you have to tell is the number reported is galon, liters, cubic centimeter, mililiter, cubir meter, or what.
