Area Units, a mathematical concept, refers to the units that measure the surface size of an object. The unit rate is 100 decimal, and the commonly used area units are cm_ (square centimeter) and m_ (square meter).
1cm_ (square centimeter) is about as big as the surface of the thumb nail;
1dm_ (square decimeter) is probably the face of the socket head, as big as the palm of your hand;
1m_ (square meter) is about the desktop size of a heating table and a mahjong table.