Is zillion a number

No, zillion is not a formally defined number in mathematics—it's an informal term used to describe an extremely large, indefinite quantity. Unlike million, billion, or trillion, which have precise numerical values, "zillion" is colloquial language people use when they want to emphasize an amount too large to count or specify exactly.

In everyday conversation, you might hear someone say "I've told you a zillion times" or "this will cost a zillion dollars" as hyperbole. The term serves a rhetorical purpose rather than a mathematical one, similar to words like "gazillion," "bajillion," or "umpteen." While children sometimes ask about zillion's numerical value and it appears in casual speech, no scientific, financial, or academic context would use "zillion" in formal calculations or documentation. For actual large numbers beyond trillion, mathematics uses defined terms like quadrillion, quintillion, and sextillion, each with specific values and zero counts.