a ride on someone's back with your arms round the person's neck and your legs round their waist

I gave her a piggyback ride. 我背着她。

on someone's back, or on the back of something

Martha rode piggyback on her dad. 玛莎骑在她爸爸的背上。

Dom carried his daughter piggyback when she got too tired to walk. 女儿累得走不动时，多姆就背着她走。

to use something that someone else has made or done in order to get an advantage

Everyone wants to piggyback on the phenomenal success of the TV series. 每个人都想借这部电视连续剧大获成功的机会沾点光。