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top and bottom; up and down; high and low; above and below; upper and lower ends
upside-down
「上下」 has other readings with different meanings.
エレベーターが上下に動いて人を運ぶ。
The elevator moves up and down to carry people.
株価が上下して投資家を不安にさせた。
Stock prices fluctuated up and down, making investors anxious.
この機械は上下に動かすと電源が入る。
If you move this machine up and down, it turns on.