Plural of 'dia,' a slide used in a projector, or in some contexts, a raised platform or stage area.
From Latin 'dies' meaning 'day,' or from Spanish/Portuguese where 'día' means day. In English, 'dia' became a shorthand term for 'diapositives,' the technical name for photographic slides.
Before digital cameras and PowerPoint, photographers and teachers used slides—'dias'—which had to be loaded into special projectors and carefully arranged in the right order! Collectors of vintage slides can find some beautiful artistic photography from the 1950s-1980s.
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