As an adjective, it means related to the outer edges of something, or not central and less important. As a noun, it can mean a device connected to a computer, like a mouse or printer.
From Greek “periphereia” meaning “circumference, outer surface,” from “peri-” (around) + “pherein” (to carry). It kept the idea of being around the outside rather than at the center.
Your ‘peripheral vision’ is what you see out of the corner of your eye, not in sharp focus. In computers, a ‘peripheral’ is literally something around the main unit—extras at the edges of the system.
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