Very large amounts of something, especially written material or paper (a ream is specifically 500 sheets of paper).
From Arabic 'rizmah' (bundle of paper), which entered English through Spanish and Italian traders. Originally meant a standard bundle used in the paper trade.
A ream of paper has exactly 500 sheets because of medieval Arabic traders—they standardized it, and we've kept the same number for centuries, even though 'ream' now just means 'tons of stuff'!
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