a number equal to 1 followed by 45 zeros (or 10 to the 45th power)
About the word:
The -illion part is modeled on million; the quattuordec comes from the Latin word for fourteen. Why 14? Because there are 14 groups of three zeros after the number 1,000 in quattuordecillion.
Many denominations above one million have names that indicate the number of groups of three zeros after the number 1,000. Centillion, for instance, represents 100 groups of three zeros after 1,000 (303 zeros).