Why do they use the symbol 2 for the word square in geometry area?

When you multiply numbers with units you must not only multiply the numbers but the units must be treated as if multiplied, so the answer has the correct units. For example, to get the area of a rectangle which is 3 in. by 5 in. you would multiply and write the answer; 15 in. in. Since you have the unit "in." multiplied by itself its called inches squared, or you can use the shorter notation in^2 ,which means the same thing, since any symbol raised to the 2 power means multiply it by itself.