Is 1 octillion a real number

Yes, 1 octillion is a real number with a precise mathematical definition. In the short scale system (American/modern international usage), 1 octillion equals 10^27—that's 1 followed by 27 zeros. In the long scale system (historical European), it equals 10^48.

However, "real number" in your question likely means "actually used number" rather than the mathematical category of real numbers (which includes all rational and irrational numbers). While octillion is mathematically defined and real, it has virtually no practical applications. You'll never encounter octillion-scale quantities in economics, everyday measurements, or most sciences. Even in cosmology, where extremely large numbers appear, scientists prefer scientific notation (10^27) rather than saying "octillion." The number exists in the systematic naming convention that extends indefinitely, but beyond trillion or perhaps quadrillion, these names become mathematical curiosities rather than practical tools.