Is 7 zillion a number

No, "zillion"—whether 7 zillion or any other number of zillions—is not a mathematically defined number. It's an informal colloquial term people use to indicate an extremely large, indefinite quantity without specifying an exact amount. Therefore, "7 zillion" is simply hyperbole multiplied by 7, but still without any precise numerical value.

In casual conversation, someone might say "I have 7 zillion things to do today" as exaggeration, but this has no mathematical meaning. Unlike million (10^6), billion (10^9), or trillion (10^12), which have exact values, "zillion" and its multiples serve purely rhetorical purposes. For actual large numbers, mathematics provides systematic terminology: thousand, million, billion, trillion, quadrillion, quintillion, and so forth, each with precise values. If precision matters in your context—whether discussing quantities, measurements, or financial figures—avoid terms like "zillion" and use properly defined numbers instead. "Zillion" belongs to informal speech and exaggeration, not mathematics, science, or any technical field requiring accurate quantification.