A cap or covering attached to the back part of something, especially a lens cap that covers the rear of a camera lens.
From 'back' + 'cap' (a head covering or removable lid). This is modern technical jargon combining everyday words to describe a protective covering on the back-facing side of equipment.
Camera caps seem simple, but photographers learned hard lessons about sensor dust—that tiny plastic backcap protects a sensor worth hundreds of dollars from invisible particles floating in air.
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