When we multiply a number by itself we are raising it to a power. And in math we use an exponent to show that a number has been raised to a power. For example: 7 x 7 means that we have raised the number 7 to the second power.
Or 7 x 7 x 7 means that we have raised 7 to the third power. But instead of writing the number 7 over and over, we use exponents to show how many times the number is a factor.