By M2 I presume you mean meters squared. It is commonly written as M^2, or M followed by a small 2 which has been raised above the M. A meter squared is the scientific unit for area. It is defined as the area of a square, where all four sides have a length of exactly 1 meter (roughly 39 inches). 1 meter squared is exactly equal to 10,000 cm squared. This is because the area of a square is base times height. So a square with sides of length 1 meter has an area of 1m * 1m = 1 meter squared. Alternatively, since 1m is equal to 100cm, you could imagine the same square being made up of sides 100cm in length. By the same calculation 100cm*100cm = 10,000cm squared. The "squared" part of meters squared simply means that the unit has come from the unit meters * meters. For example volume, which is made up from meters * meters * meters, is known as meters cubed. Centimetres cubed would therefore be made up of cm * cm * cm.
M2 is the area metric units (SI Unit), which is defined as: The length of 1 meter square area.