Every unit of length has a corresponding unit of area, namely the area of a squarewith the given side length. Thus areas can be measured in square metres (m2), square centimetres (cm2), square millimetres (mm2), square kilometres (km2), square feet (ft2), square yards (yd2), square miles (mi2), and so forth.
so, to shorten it down, its a little number 2.
https://en.wikipedia.org/wiki/Area
