1The back of a person or animal's body, from below the neck down to the waist. Also called 背中.
重い荷物を背に負って山道を歩いた。
I carried heavy luggage on my back as I walked the mountain trail.
子どもが父親の背に乗って喜んでいる。
The child is delighted riding on his father's back.
彼はまっすぐな背筋を伸ばして立っていた。
He stood with his back straight and his posture upright.
背にリュックを担いで、電車に乗った。
I got on the train with a backpack on my back.
2The reverse or rear side of an object — such as the back of a chair or the bound edge of a book (its spine).
この椅子の背は高くて、頭までしっかり支えてくれる。
The back of this chair is tall and supports you all the way up to your head.
本棚から探すときは、背にある書名を見るといい。
When looking for a book on the shelf, it helps to check the title on the spine.
カードの背に署名欄がある。
There's a signature strip on the back of the card.
3A person's height or stature. Most often used in expressions like 背が高い/低い ('tall/short').
弟は最近急に背が伸びて、私よりも高くなった。
My little brother suddenly grew taller recently and is now taller than me.
背が高い人はバスケットボールに向いていると言われる。
Tall people are said to be well suited for basketball.
昔は背が低いのを気にしていたが、今はもう気にしない。
I used to worry about being short, but I don't care anymore.
4The ridge of a mountain — the crest connecting its peaks, as in 山の背.
登山道は山の背に沿ってどこまでも続いていた。
The mountain trail continued endlessly along the ridge.
稜線の背に立つと、遠くの街まで見渡せた。
Standing on the ridge, I could see all the way to a distant town.