
[Short for Middle English (in) quarto, (in) the fourth part (of a sheet), from Medieval Latin (in) quārtō, from Latin, ablative of quārtus, fourth.]
paper and printing Symbol 4to. A paper size, being ¼ of a full sheet, the actual size depending on that of the full sheet. Used very commonly in the UK to mean specifically the quarto or folio post or demy trimmed, at 8.5 in × 11 in (215.9 mm × 279.4 mm), termed letter size in North America.

Quarto is a board game for two players invented by Swiss mathematician Blaise Müller.
It is played on a 4×4 board. There are 16 unique pieces, each of which is either:
Players take turns choosing a piece which the other player must then place on the board. A player wins by placing a piece on the board which forms a horizontal, vertical, or diagonal row of four pieces, all of which have a common attribute (all short, all circular, etc.). A variant rule included in many editions gives a second way to win by placing 4 matching pieces in a 2x2 square.
Quarto is distinctive in that there is only one set of common pieces, rather than a set for one player and a different set for the other. It is therefore an impartial game.
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