what is the definition of the word "base" when the mathematical expression contains an exponent?

a. the base is the number that tells you to square a number
b. the base is the number that tells you how many times to multiply by itself
c. the base is the number being multiplied by itself a given number of times
d. the base is the biggest number in the expression

b. the base is the number that tells you how many times to multiply by itself