The number 5 is a whole number that equals 25 when it is squared and 125 when it is cubed. Five is the only number, whole or otherwise, that satisfies both of these criteria.
To square a number, multiply it by itself. Five squared is 5 times 5, which equals 25. A number cubed is multiplied by itself twice: 5 times 5 times 5 is 5 cubed, which equals 125. The terms "squared" and "cubed" come from the formulas for calculating the area of a square and the volume of a cube. The area of a square is the length of its sides squared; the volume of a cube is the length of its sides cubed.