A book size made by folding a sheet of paper into 12 leaves, or a book of this size, often abbreviated as 12mo.
From Latin 'duodecimo' meaning 'in twelfths.' The term is part of a paper-folding system used in bookbinding where 'folio' is one fold, 'quarto' is two folds, 'octavo' is three folds, and duodecimo is four folds.
Before modern printing standardized book sizes, every book was handmade, and the duodecimo became the perfect pocket-sized format—these small books were ideal for carrying poetry collections or religious texts! You can actually identify old books by their size format alone, and duodecimo represents a specific era of publishing history.
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