おんぶ (onbu) means “carrying someone on one's back”

More examples

眠ってしまった妹をおんぶで家まで運びました。nemu tte shi ma tta imōto o o n bu de ie ma de hako bi ma shi ta

I carried my little sister home on my back after she fell asleep.

Centers on supporting another person on one's back while carrying them.

背負いseoi: The act of carrying a person or load on the back while supporting its weight there.

人を背中に乗せて運ぶこと。hito o se naka ni no se te hako bu ko to

おんぶ (onbu) is linked to おぶう (obū), an older verb meaning "to carry on one's back"; the exact sound change to the modern form is uncertain.

English piggyback comes from the older phrase pick-a-back, so its sound does not refer to pigs, while おんぶ (onbu) is the usual Japanese word for this action.