It is the exponent.
The exponent is the number used in a power to represent the number of times the base is used as a power.
For example: 7^2. The number 2 is the exponent and it indicates that the number 7 (which is the base) is used two times as a factor, this is, 7^2 = 7 * 7.
Othe example: 4^6. The exponent 6 indicates that the base 4 is used 6 times as a factor => 4^6 = 4 * 4 * 4 * 4 * 4 * 4.
