For example, the square formed by the first four cells in the upper left corner is addressed as A1:B2. By addressing an area in this way, you are making a relative reference to A1:B2. Relative here means that the reference to this area will be adjusted automatically when you copy the formulae.
範囲を A1:B2 のように呼ぶことを相対参照といいます。相対とはこの場合、数式をコピーした際に参照が修正されることを意味します。