In mathematics, the set of all possible output values that a function can theoretically produce, whether or not all values are actually used.
From co- (joint, together) + domain. Coined in the 20th century as mathematical terminology to distinguish from range, the set of values actually produced.
A function's codomain is like a permission slip that says 'I can produce values from this set,' while the range is what you actually get—this distinction revolutionized how mathematicians think about functions.
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