informal Brit a ride on the back of someone's bicycle
And here the words backie or backy is listed as an "untranslatable", the blogger found no American equivalent.
The BBC have been known to use it, too:
Boris Johnson 'naughty' for giving wife backie on his bike
Of course, it could also be a "lift", but that sounds British to me and, more importantly, can be used with a car rather than a bike.
So, is there an American equivalent of a "backie"? Is it understandable to Americans? Or is there even a formal single word term in any version of English?
For context, I’d like to say something like "He gave his friend a [backie]"
More details on a "backie":
it’s done on a bicycle with no second seat. You can perch on a parcel shelf if there is one, but much more common is that the person who owns the bike stands on the pedals and the person getting the "backie" sits on the bike seats.
Some bikes are fitted with stunt pegs and the person getting the backie can stand on these if they’re available. More commonly, their legs are just splayed out to the sides.
According to the bbc link, it’s illegal. But children/teenagers do it regularly. I haven’t heard of anyone being prosecuted, but I don’t know what it would be called if they were.
I think there might be examples in Stephen King's "It" (book and Tim Curry TV version) there are occasions where 2 people ride on Silver, eg Bill and Eddie with Bill pedalling.