An indefinitely large number; a word used informally to mean 'countless' or 'way too many to count.'
American slang, probably formed from 'million' with the 'z' sound added for emphasis and playfulness, possibly influenced by words like 'gazillion.' It has no precise mathematical meaning.
There's no 'zillion' in formal mathematics, but kids naturally created it by stacking number-words—if a million has an 'm,' why not a 'z-illion'?—showing how language grows when we need to express ideas bigger than official words allow.
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