Plural of real, referring to the former monetary unit of several countries including Brazil, or in mathematics, the set of real numbers. Can also refer to actual, genuine things as opposed to artificial ones.
From Spanish/Portuguese 'real' meaning 'royal', from Latin 'regalis'. As currency, it indicated money backed by royal authority. In mathematics, 'real numbers' (contrasted with imaginary numbers) were named in the 17th century to distinguish numbers that could represent actual quantities.
The mathematical term 'real numbers' is delightfully ironic - these numbers aren't more 'real' than imaginary numbers, they're just more familiar to us. The name stuck from an era when mathematicians thought negative numbers were absurd and complex numbers were impossible, making positive rational numbers seem like the only 'real' math.
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