A photographic positive transparency, especially a color slide used for projection or viewing on a light box; a type of photographic image.
From Greek 'dia-' (through) + 'positive' (from Latin 'positivus'). The term emerged in photography around the late 1800s to distinguish transparent positives from negatives.
Diapositives were the Instagram of the mid-20th century—families gathered around projectors to show slides, and professional photographers had entire diapositive libraries worth thousands of dollars!
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