A Quire

“A quire of paper is a measure of paper quantity. The usual meaning is 25 sheets of the same size and quality; 1/20 of a ream of 500 sheets. Quires of 25 sheets are often used for machine-made paper, while 24 sheets are often used for handmade or specialised paper of 480-sheet reams. Quires of 15, 18 or 20 sheets have also been used, depending on the type of paper.

“In the Middle Ages, a quire (also called a ‘gathering’) was most often formed of 4 folded sheets of vellum or parchment, i.e. 8 leaves, 16 sides. The term ‘quaternion’ (or sometimes quaternum) designates such a quire. A quire made of a single folded sheet (i.e. 2 leaves, 4 sides) is a ‘bifolium’ (plural ‘bifolia’); a ‘binion’ is a quire of two sheets (i.e. 4 leaves, 8 sides); and a ‘quinion’ is five sheets (10 leaves, 20 sides). This last meaning is preserved in the modern Italian meaning of quire, quinterno di carta.

“The current word ‘quire’ derives from OE ‘quair’ or ‘guaer’, from OF ‘quayer’, ‘cayer’, (cf. modern Fr. cahier), from L. quaternum, ‘by fours’, ‘fourfold’.

“The printer William Caslon in a book published in 1770 mentions both 24- and 25-sheet quires ….

“It also became the name for any booklet small enough to be made from a single quire of paper. Simon Winchester, in The Surgeon of Crowthorne, cites a specific number, defining quire as ‘a booklet eight pages thick.’ Several European words for quire keep the meaning of ‘book of paper.'”

From Wikipedia