backie       
noun [ C ] UK informal uk/ˈbæk.i/ us/ˈbæk.i/
 搭坐在自行车后座上
a ride given to someone who sits behind you on your bicycle
  He gave me a backie. 他让我坐在自行车后座上,捎了我一程。 
 - More examples
- Can I have a backie to the park?
- We were banned from giving backies.