APS-C is a size of image sensor used in many digital cameras. Most APS-C sensors measure about 23.5 x 15.6 mm. Canon's version is a little smaller, about 22.3 x 14.9 mm. The aspect ratio is 3:2, and the crop factor is about 1.5 (1.6 for Canon) compared with full frame.
The name comes from the Advanced Photo System, a film format launched in 1996. Its "C" (Classic) frame measured 25.1 x 16.7 mm. APS film was discontinued in 2011.
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