Saw this on a charger I bought online and was really perplexed. What foreign word does it represent? "concentric"? What does that have to do with outlet and where did it come from?
It is 和製英語. Sometime around the 1920s, employees at 東京電燈会社 created a device which consisted of a plug and outlet. This was called コンセントプラグ "concentric plug". Outlets without the plugs are now referred to as コンセント. Needless to say, English "concentric" does not make much sense.
It comes from concentric plug. Although the origin is not 100% clear, it appears that plugs were round (concentric) in early 20th century England, which may be where the word comes from.