500 sheets of paper, regardless of size More specifically, a ream is 20 quires of paper A quire is 24 or 25 sheets of paper, making a ream of paper 480 or 500 sheets However, quire is an archaic unit; in modern usage, a ream is 500 sheets
a quantity of paper; 480 or 500 sheets; one ream equals 20 quires a large quantity of written matter; "he wrote reams and reams" enlarge with a reamer; "ream a hole" remove by making a hole with a reamer; "ream paper" squeeze the juice out (of a fruit) with a reamer; "ream oranges