To solve this question, the user needs to have knowledge of numerical prefixes and their meanings.

Each option is a numerical prefix, followed by a noun that indicates a quantity. The user must identify the prefix that describes a very large, indefinite number.

A. Trillion: This option is a numerical prefix that indicates one million million or 10^12. While this is a large number, it is not necessarily considered indefinite.

B. Million: This option is a numerical prefix that indicates one thousand thousand or 10^6. While this is a large number, it is not considered indefinite.

C. Zillion: This option is not a standard numerical prefix and does not have a specific value. It is usually used informally to indicate an extremely large number.

D. Billion: This option is a numerical prefix that indicates one thousand million or 10^9. While this is a large number, it is not necessarily considered indefinite.

Therefore, the correct answer is:

The Answer is: C